revised road safety design manual - june 1, 2011

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Highway Safety Design Standards

Part 1:

Road Safety DesignManual

May 2011

Republic of the PhilippinesDEPARTMENT OF PUBLIC WORKS AND HIGHWAYS



May 2004 Road Safety Design Manual ii

FOREWORD

This Road Safety Design Manual is issued by the Department of Public Works andHighways (DPWH) to establish and maintain standardized safe road designprinciples and standards for roads in the Philippines.

The manual is part of the DPWH Highway Safety Design Standards Manual asfollows:

Part 1: Road Safety Design Manual

Part 2: Road Signs and Pavement Markings Manual

This Road Safety Design Manual has been developed as part of the RoadInfrastructure Safety Project with the assistance of DPWH staff from the Bureau ofDesign and the Road Safety Section, Project Evaluation Division of the PlanningService.

This manual is to be used in conjunction with the DPWH Highway Design Guidelines.The manual includes standards and guidance for safety planning, safety design andfor road safety risk assessment. The manual is to be used as a primary reference forthe planning, design and management of National Highways and local roads. Tomaximize safety, it is essential to maintain a consistent standard for road andintersection design.

In the interests of uniformity, Local Government Units, project managers andconsultants are requested to apply the principles in this manual to provideappropriate standards for intersections and lengths of roadway in the Philippines.The principles contained in this manual should also be used in the training of DPWHstaff involved in road planning, design, road works project management and trafficmanagement.

The manual includes safety design principles based on best international practiceapplicable to the Philippines settings. Specific areas of design where changes inpast practice are expected to lead to significant safety improvements include:

Choice of intersection type and layout. This is particularly related to thedesign and use of roundabouts and the type of channelization to reducepotential conflicts and the severity of traffic accidents (includes avoidinguse of ‘Y’ junctions and ‘T’ junctions with triangular islands);

Safety of the roadside. This includes the definition of a ‘clear zone’ for aforgiving roadside and the use of certified median and roadside barriersas well as the use of frangible lighting poles; and

Safety of unprotected road users such as pedestrians and cyclists.

When the design principles in this manual are used in conjunction with the DPWHHighway Design Guidelines, roads and intersections will be to a design thatmaximizes road safety.



May 2004 Road Safety Design Manual iii

References:

AASHTO - A Policy on Geometric Design of Highways and Streets, 2001.

AASHTO - Roadside Design Guide, 2002.

U.S. Highway Capacity Manual.VicRoads – Road Design Guidelines.

AUSTROADS – Rural Road Design: A Guide to the Geometric Design of RuralRoads, 2003.

AUSTROADS – Urban Road Design: A Guide to the Geometric Design of MajorUrban Roads, 2002.

AUSTROADS –Guide to Traffic Engineering Practice, Part 5: Intersections at Grade.

AUSTROADS –Guide to Traffic Engineering Practice, Part 6: Roundabouts.



May 2004 Road Safety Design Manual iv

Table of Contents

FOREWORD ............................................................................................................................. II SAFETY PLANNING ................................................................................................................. 1

1 INTRODUCTION ............................................................................................................... 2 1.1 Background .......................................................................................................... 2

2 LAND USE AND ZONING ................................................................................................... 3 2.1 Principles in Land Use Planning and Zoning ............................... ........................ 4 2.2 Traffic Planning for Different Land Uses ...................................... ........................ 5

2.2.1 Residential Areas ......................................................................................................... 5 2.2.2 Industrial Areas ............................................................................................................ 6 2.2.3 Commercial / Retail Areas ............................................................................................ 6 2.2.4 Recreational/Tourism Areas ......................................................................................... 7

3 ROAD HIERARCHY ...................................... ....................................... .............................. 9 3.1 Primary Arterials (Expressways, National Roads) ................................... .......... 10

3.2 Secondary Arterials (Provincial Roads) ............................................................. 11 3.3 Collector Roads (Municipal / City Roads) .................................... ...................... 12 3.4 Access Roads (Local Roads) ............................................................................ 13 3.5 Pedestrianized Areas/Routes ............................................................................ 15

4 ROUTE P LANNING THROUGH EXISTING COMMUNITIES ............................... ...................... 17 5 DEVELOPMENT CONTROL / ENCROACHMENT .................................................................. 19 6 ACCESS CONTROL ........................................................................................................ 20 7 TRAFFIC IMPACT ASSESSMENT (TIA) ............................................................................. 21 8 ROAD DESIGN P ARAMETERS ......................................................................................... 23

8.1 Speed Management........................................................................................... 23 8.1.1 Design Speed ............ ............ ............. ........... ............. ............ ............. ........... ............ 23 8.1.2 Speed Implications ..................................................................................................... 23 8.1.3 Current Speed Limits .................................................................................................. 23 8.1.4 Speed Restriction Signs ............................................................................................. 26 8.1.5 Poor Road Standards ................................................................................................. 26

8.2 Road Capacity ................................................................................................... 26 8.3 Traffic Forecasts ................................................................................................ 27

9 P UBLIC TRANSPORT ...................................................................................................... 28 9.1 Public Transport Operations .............................................................................. 28 9.2 Lay-bys, Bus Stops and Service Roads ............................................ ................ 28

10 VULNERABLE ROAD USERS ........................................................................................... 31 10.1 Pedestrians ........................................................................................................ 34 10.2 Cyclists ............................................................................................................... 36

11 P ARKING ...................................................................................................................... 38 11.1 Parking Near Intersections ................................................................................ 38 11.2 Angle Parking ......................................... ...................................... ...................... 38 11.3 Parking Adjacent To Barrier Lines ..................................................................... 39

12 LIGHTING ...................................................................................................................... 41 SAFETY DESIGN .................................................................................................................... 44

13 INTRODUCTION ............................................................................................................. 45 13.1 Background ..................................... ....................................... ............................ 45 13.2 Safe Design Principles ....................................... ...................................... .......... 45

14 ROAD S URFACE ............................................................................................................ 46 15 ROAD ALIGNMENT CONSIDERATIONS ............................................................................. 48

15.1 Introduction ........................................................................................................ 48 15.2 Some Physical Problems ......................................... ...................................... .... 48



May 2004 Road Safety Design Manual v

16 ROAD ALIGNMENT GEOMETRY ....................................... ...................................... .......... 55 16.1 General .............................................................................................................. 55 16.2 Design Standards .............................................................................................. 56 16.3 Sight Distance ................................. ....................................... ............................ 58

16.3.1 Introduction ............................................................................................................ 58 16.3.2 Sight Distance Elements ........................................................................................ 58 16.3.3 Driver Eye Height / Object Height .......................................................................... 59 16.3.4 Stopping Sight Distance (SSD) .............................................................................. 59

16.4 Horizontal Geometry .......................................................................................... 62 16.4.1 Circular Curve Alignment ....................................................................................... 62 16.4.2 Spiral and Circular Curve Alignment ...................................................................... 63 16.4.3 Superelevation Development ................................................................................. 65

16.5 Vertical Geometry .............................................................................................. 66 16.5.1 Grades ................................................................................................................... 66 16.5.2 Vertical Curves ...................................................................................................... 69

17 CROSS SECTION ........................................................................................................... 74 17.1 Introduction ........................................................................................................ 74 17.2 Traffic Lanes ...................................................................................................... 74 17.3 Shoulders ........................................................................................................... 75 17.4 Curb and Gutter ................................................................................................. 75 17.5 Drainage ............................................................................................................ 76

17.6 Pedestrian Facilities on Rural Roads ..................................... ............................ 77 17.7 Overtaking Provision (Auxiliary Lanes) .................................. ............................ 78 17.7.1 Overtaking Lanes: ................................................................................................. 79 17.7.2 Climbing Lanes ............. ........... ............. ............. ............ ............. ........... ............. ... 81 17.7.3 Merging and Diverging for Auxiliary Lanes ............................................................ 82 17.7.3 Slow Vehicle Turn-outs: ......................................................................................... 83 17.7.4 Descending Lanes: ............. ............ ............. ........... ............. ............ ............. ......... 84 17.7.5 Emergency Escape Ramps: .................................................................................. 84

18 DELINEATION ................................................................................................................ 86 19 INTERSECTIONS ............................................................................................................ 89

19.1 Intersection Types .................................. ...................................... ...................... 89 19.2 Traffic Control Devices....................................................................................... 89

19.2.1 Priority Intersections .............................................................................................. 90 19.2.2 Signal Controlled Intersections .............................................................................. 90

19.3 Control of Conflicts ....................................... ...................................... ................ 90 19.4 Control of Speed ................................................................................................ 92 19.4.1 Relative Speed ...................................................................................................... 92

19.4.2 Attaining low relative speeds ................................................................................. 93 19.5 Channelization ................................................................................................... 94 19.6 Lane widths ..................................... ....................................... ............................ 95 19.7 Auxiliary Lanes at Intersections ..................................... .................................... 95 19.8 Right and Left Turning Lanes ............................................................................ 96 19.9 Right Turn Slip Lanes ........................................................................................ 98

19.8.1 High Entry Angle Slip Lane .................................................................................... 99 19.8.2 Free Flow Slip Lane ............................................................................................. 100

19.10 Left Turn Treatments ..................................... ...................................... ........ 100 19.11 Intersection Capacity ..................................... ...................................... ........ 102 19.12 Sight Distance at Intersections .................................. .................................. 102 19.13 Horizontal and Vertical Intersection Geometry .................................... ........ 103 19.14 Roundabouts ............................................................................................... 104

19.14.1 Introduction ............ ............. ........... ............. ............. ............ ............. ........... ............. . 104 19.14.2 Safety Benefits ........................................................................................................... 104 19.14.3 Appropriate Locations for Roundabouts .................................................................... 104 19.14.4 Balanced Flows ......................................................................................................... 105 19.14.5 Roundabout Design Practice ..................................................................................... 105 19.14.6 Things to Avoid .......................................................................................................... 109 19.14.7 Design Steps ............................................................................................................. 109 19.14.8 Traffic Control and Priority ......................................................................................... 113



May 2004 Road Safety Design Manual vi

19.15 Examples of Poor Intersection Layouts ................................... .................... 114 19.15.1 Y-Intersection ............. ............ ............. ........... ............. ............ ............. ........... .......... 114 19.15.2 ‘Y’ Intersection with Triangular Island ........................................................................ 116

20 S AFETY OF THE ROADSIDE .......................................................................................... 117 20.1 Introduction ...................................................................................................... 117 20.2 Clear Zone ....................................................................................................... 117

20.3 New Roads ...................................................................................................... 121 20.4 Existing Roads ................................................................................................. 121 20.5 Treatment of Hazards ...................................................................................... 122 20.6 Roadside and Median Safety Barriers ........................................................... .. 126

20.6.1 Road Safety Barrier Systems: ............................................................................. 127 20.6.2 Design Of Barrier System Installations ................................................................ 133

20.7 Further Examples of Barrier Installations......................................................... 140 20.7.1 Bridge Railing ...................................................................................................... 140 20.7.2 Connection to Bridge Railing ............................................................................... 141 20.7.3 Railing End Treatment ......................................................................................... 142 20.7.4 Unconnected Concrete Barriers .......................................................................... 143 20.7.5 Gore Area ............................................................................................................ 145 20.7.6 Trees ................................................................................................................... 147 20.7.7 Street Lighting Poles............................................................................................ 147 20.7.8 Other Examples of Roadside Hazards................................................................. 150 20.7.9 Curbs in Front of Barriers .................................................................................... 152

RISK ASSESSMENT ............................................................................................................ 153 21 RISK ASSESSMENT ..................................................................................................... 154

21.1 Risk .................................................................................................................. 154 21.2 Likelihood ......................................................................................................... 154 21.3 Consequence ......................................... ...................................... .................... 154 21.4 Risk Category .................................................................................................. 155 21.5 Treatment Priority ............................................................................................ 155

APPENDIX 1 - ROADSIDE BARRIERS STANDARD DRAWINGS

APPENDIX 2 - CONCRETE BARRIERS

APPENDIX 3 - FRANGIBLE POLES - SPECIFICATION AND DRAWINGS

APPENDIX 4 - SPEED TEMPLATES FOR ROUNDABOUT DESIGN

APPENDIX 5 - TURNING TEMPLATES FOR LARGE VEHICLES

APPENDIX 6 - CONCRETE CURB AND GUTTER DETAILS



May 2004 Road Safety Design Manual vii

Table of Figures

Figure 2.1 : Poor Zoning and Road Planning Interface ................................................ 4 Figure 2.2 : Good Zoning and Road Planning Interface ............................................... 5 Figure 2.3 : Ideal Road Network Planning for Tourism Areas ...................................... 8

Figure 3.2 : Externally and Internally-fed Networks .................................................... 10 Figure 3.3 : Road Network that Attracts Through Traffic Onto Local Roads .............. 14 Figure 3.4 : Road Network that Deters Through Traffic from Using Local Road........ 14 Figure 3.5 : Road Layouts that Deters Through Traffic from Using Local Roads ...... 15 Figure 4.1 : Road Layout that Results in Conflict Between Local and Through Traffic

................................................................................................................ 18 Figure 4.2 : By Pass Road Deters Through Traffic from the Community ................... 18 Figure 5.1 : Encroachment that Reduces Effective Sidewalk Width........................... 19 Figure 8.1 : Risk of Pedestrian Fatality ....................................................................... 24 Figure 8.2 : High Speed Road with Separate Lane for Non-Motorized Vehicles ....... 25 Figure 8.3 : High Speed Road with Wide Median ....................................................... 26 Figure 9.1 : Bus Stop Concept, EDSA ........................................................................ 29 Figure 9.2 : Lay-By Concept, EDSA ............................................................................ 29 Figure 10.1 : Poor facilities for pedestrians ................................................................. 34 Figure 10.2 : Good Pedestrian Facilities ..................................................................... 35 Figure 10.3 : Obstructions that Reduce Effective Travel Width for Pedestrians ........ 36 Figure 10.4 : Segregated Pedestrian and Bikeway from Main Thoroughfare ............ 36 Figure 10.5 : Road without bike lanes ......................................................................... 37 Figure 11.1 : Angle Parking with Maneuvering Area Clear of Through Traffic Lanes 39 Figure 12.1 : Types of Lighting and Illumination ......................................................... 42 Figure 12.2 : Lighting Installations at Intersections ..................................................... 43 Figure 14.1 : Poor road surface with depressed manhole lid ..................................... 46 Figure 14.2 : Poor Road Edge ..................................................................................... 47 Figure 15.1 : Poor Design and Delineation of Curve .................................................. 48 Figure 15.2 : Lost Control on Curve ............................................................................ 49 Figure 15.3 : Extreme topography results in small radius curves ............................... 49 Figure 15.4 : Trees Obstructing Sight Distance .......................................................... 50 Figure 15.5 : Poor Vertical Alignment Approaching a T-Intersection ......................... 50 Figure 15.6 : Poor Intersection due to Lack of Channelization ................................... 51 Figure 15.7 : Small (5m radius) Roundabout in Balayan Town .................................. 51 Figure 15.8 : Horizontal Curve at the End of a Steep Downgrade ............................. 52 Figure 15.9 : Poor Vertical Sag ................................................................................... 52 Figure 15.10 : Reverse Curves .................................................................................... 53 Figure 15.11 : Poor Combination of Horizontal and Vertical Alignment ..................... 53 Figure 15.12 : Delineation of Curve – Poor night-time visibility .................................. 54 Figure 16.1 : Sight Distance Types ............................................................................. 61 Figure 16.2: Circular Curve Geometry ........................................................................ 63 Figure 16.4: Superelevation Development .................................................................. 65

Figure 16.5: Truck Speeds on Grades ........................................................................ 68

Figure 16.7 : Crest Vertical Curves ............................................................................. 71 Figure 17.1 : Good Cross-Section providing lane for vulnerable road users. ............ 74 Figure 18.1 : Good Road Delineation .......................................................................... 86 Figure 18.2 : Poor Curve Delineation .......................................................................... 87 Figure 18.3 : Poor Delineation of the Center and Edge of Roadway ......................... 87 Figure 18.4 : Examples of Chevron Signs providing Delineation of Curves ............... 87 Figure 18.5 : Road Delineation affected by shadows ................................................. 88 Figure 19.1 : Large Intersection Conflict Area............................................................. 91 Figure 19.2 : Three-Legged Intersection ..................................................................... 91



May 2004 Road Safety Design Manual viii

Figure 19.3 : Four-Legged Intersection ....................................................................... 91 Figure 19.4 : Roundabout at Four-Legged Intersection .............................................. 92 Figure 19.5 : Cross Road ............................................................................................. 92 Figure 19.6 : Y Intersection Layout ............................................................................. 93 Figure 19.7 : Roundabout ............................................................................................ 93 Figure 19.8 : Conflicts at Y and T Intersections .......................................................... 94 Figure 19.9 : Guideline for Left and Right Turn Lanes ................................................ 96 Figure 19.10 : High Entry Angle Slip Lane .................................................................. 99 Figure 19.11 : Free Flow Slip Lane ........................................................................... 100 Figure 19.12 : Type A Left Turn Treatment .............................................................. 101 Figure 19.13 : Type B Left Turn Treatment ............................................................... 101 Figure 19.14 : Type C Left Turn Treatment ............................................................... 101 Figure 19.15 : Geometric Elements of a Roundabout............................................... 105 Figure 19.16 : Inner Urban Roundabout.................................................................... 106 Figure 19.17 : Outer Urban Roundabout ................................................................... 107 Figure 19.18 : Rural Roundabout .............................................................................. 107 Figure 19.19 – Urban Splitter Island Details : Low Speed Approach ....................... 108 Figure 19.20 : Urban Splitter Island ........................................................................... 108 Figure 19.21 : Splitter Island for High Speed Approach ........................................... 109

Figure 19.22 : Movement Volumes and Circulating Flows ....................................... 109

Figure 19.23 : Number of Lanes ................................................................................ 110 Figure 19.24 : Turning Radius for Determining Circulating Carriageway Width ....... 110 Figure 19.25 : Deflection Requirement – Single lane ............................................... 112 Figure 19.26 : Deflection Criteria – Multi Lane .......................................................... 112 Figure 19.27 : Typical Pavement Markings at a Multi Lane Roundabout ................. 113 Figure 19.28 : Give Way Sign (R1-2) ........................................................................ 114 Figure 19.29 : Poor Intersection Layout .................................................................... 114 Figure 19.30 : Poor delineation ................................................................................. 115 Figure 19.31 : Poor Intersection Layout .................................................................... 116 Figure 20.1 : Recovery Area (100 kph operating speed, flat cross slope) ............... 118 Figure 20.2 Road with Good Clear Zone. ................................................................ 119 Figure 20.3 : Clear Zone Calculation ......................................................................... 120

Figure 20.4 : Relocated Pole ..................................................................................... 122 Figure 20.5 : Drivable Culvert End ............................................................................ 122 Figure 20.6 : Steel Sign Posts ................................................................................... 123 Figure 20.7 : Frangible Wooden Posts ...................................................................... 123 Figure 20.8 : Pole Hazard .......................................................................................... 124 Figure 20.9 : Impact Absorbing Pole ......................................................................... 124 Figure 20.10 : Unprotected Roadside Hazard........................................................... 125 Figure 20.11 : Use of Barrier ..................................................................................... 125 Figure 20.12 : Median Barriers .................................................................................. 128 Figure 20.13 : Roadside Barriers............................................................................... 129 Figure 20.14 : Roadwork Barriers.............................................................................. 130 Figure 20.15 : Effective Clear Zone (ECZ) ................................................................ 134 Figure 20.16 : Fill Slope Safety Barrier Warrant ....................................................... 135

Figure 20.17 : Median Safety Barrier Warrant .......................................................... 136 Figure 20.18 : Approach Barrier Design Elements ................................................... 137 Figure 20.20 : Poor Bridge Railing ............................................................................ 140 Figure 20.21 : Very Good Bridge Railing................................................................... 140 Figure 20.22 : Poor Bridge Railing – No Connection ................................................ 141 Figure 20.23 : Good Connection to Bridge Railing ................................................... 141 Figure 20.24 : Poor End Treatment ........................................................................... 142 Figure 20.25 : Car Speared by Guardrail .................................................................. 142 Figure 20.26 : Very Good End Treatment ................................................................. 143 Figure 20.27 : Unconnected Concrete Barriers......................................................... 143



May 2004 Road Safety Design Manual ix

Figure 20.28 : Good Connected Barriers .................................................................. 144 Figure 20.29 : Very Good Connected Barrier ............................................................ 144 Figure 20.30 : Poor Unconnected Barrier ................................................................. 145 Figure 20.31 : Poor Gore Treatment ......................................................................... 145 Figure 20.32 : Poor Gore Treatment ......................................................................... 146 Figure 20.33 : Very Good Gore End Treatment using Impact Attenuator ................ 146 Figure 20.34 : Tree Hazard ....................................................................................... 147 Figure 20.35 : Frangible Poles .................................................................................. 147 Figure 20.36 : Impact-Absorbing Pole ....................................................................... 148 Figure 20.37 : Impact Behavior - Slip Base and Impact Absorbing Poles ................ 149 Figure 20.38 : Hazardous Roadwork Site ................................................................. 150 Figure 20.39 : Hazardous Pipe Installation ............................................................... 150 Figure 20.40 : Hazardous Protruding Pole Outside Line of Barrier .......................... 151 Figure 20.41 : Hazardous Barrier System ................................................................. 151 Figure 20.43 : Curb in front of Barrier ........................................................................ 152



May 2004 Road Safety Design Manual x

List of Tables

Table 16.1 : Design Standards for Philippine National Highways .............................. 57 Table 16.2 : Driver Eye and Object Heights ................................................................ 59 Table 16.3 : Stopping Sight Distance (SSD) ............................................................... 60 Table 16.4 : K Values for Crest and Sag Vertical Curves ........................................... 73

Table 17.1 : Traffic Volume Guidelines for Provision of Overtaking Lanes ................ 80 Table 17.2 : Overtaking Lane Lengths ........................................................................ 81 Table 17.3 : Diverge and Merge Lengths .................................................................... 83 Table 19.1 : Intersection Sight Distance (ISD) .......................................................... 103 Table 19.2 : Circulating Carriageway Widths ............................................................ 111 Table 20.1 : Curve Correction Factor ........................................................................ 121 Table 20.2 : Test Levels for Roadside Barriers ......................................................... 126 Table 20.3 : Offset from edge of traffic lane to face of barrier .................................. 132 Table 20.4 : Clearance from face of barrier to face of hazard .................................. 132 Table 20.5 : Runout Lengths for Barrier Design ....................................................... 137 Table 20.6 : Maximum Flare Rates for Barrier Design.............................................. 139 Table 21.1 : Likelihood Definition .............................................................................. 154 Table 21.2 : Consequence Definition ........................................................................ 155

Table 21.3 : Risk Category ........................................................................................ 155 Table 21.4 : Treatment Priority .................................................................................. 155



May 2004 Road Safety Design Manual 1

SAFETY PLANNING



2May 2004 Road Safety Design Manual

1 INTRODUCTION

1.1 Background

This section of the manual describes features relating to the safety of a lengthof road or the road network through the awareness of safety principles duringthe planning stages of a new area or of a road project.

Planning of new areas or road projects can be considered in four stages:

Laying out the land-use of the area. This is where for example,industrial areas can be separated from residential areas or whereconsideration should be given to the movement of people, particularlypedestrians and cyclists. The location of shopping centers and schoolsshould be considered carefully to facilitate the safe movement ofpedestrians and motor vehicles and in order to avoid the potentialimpact of adjacent heavy through-traffic;

Once the land-use is determined, an arterial road network should bedefined to cater for through traffic. This is then supported by a networkof local roads that provide access to the properties within the area.The separation of through traffic from local traffic is an importantprinciple in road safety;

On the arterial roads, careful control and management of access canfacilitate safety and the smooth flow of traffic; and,

Careful planning and provision of public transport facilities can ensurethat the conflict areas between pedestrians and vehicles areminimized.




2 LAND USE AND ZONING

Zoning in the Philippines has been under total control of the Housing andLand Use Regulatory Board (HLURB), until the early 1990’s when thisfunction was gradually decentralized to the Local Government Units by virtueof the Local Government Code. Since then, each unit of the LocalGovernment became responsible for zoning of their respective jurisdictionsand final land use and zoning plans were submitted to HLURB for approval.Thus, the municipal, city, and provincial planning and development offices(MPDO, CPDO, and PPDO) have developed comprehensive land use anddevelopment plans to control within sustainable limits urbanism and rapidgrowth.

It is the intent of this manual that road safety concerns should be givenemphasis in the conduct of traffic impact assessment for new developmentsor any project that would significantly affect local zoning ordinances. Asexperienced in Metro Manila, the emergence of large traffic generators suchas malls and similar commercial establishments has created fragmented landuse interactions that have deteriorated traffic operation of the road network.While traffic impact assessments may have been prepared for thesedevelopments, safety may not have been given adequate emphasis.Therefore, in the course of planning for large traffic generators, it is imperativeto consider the following:

That big land developments must carefully follow project size thresholdas identified by the zoning administrator of the locality. The thresholdmay be gauged based on the total land area of the project site, thefootprint area of the building, percentage land occupancy, floor arearatio (FAR);

Large land developments usually are big traffic generators and shouldnot have direct access to a high speed road facility. This is to providea buffer between pedestrians and entering traffic from high volume andhigh speed traffic;

The minimum local standards pertaining to access and parkingrequirements should be carefully followed. It may be essential thataccess, parking, and lay-by facilities must be treated separatelycorresponding to private cars, public utility vehicles, and cargotrucks/delivery vans;

Pedestrians should be given utmost consideration by providingfacilities that would segregate them from through and local traffic. Anetwork of at-grade and elevated walkways should be properly plannedconsidering travel patterns and volume of pedestrians;

Nighttime operation is deemed more critical than daytime as this wouldrequire further analysis on lighting requirements and added security;




2.1 Principles in Land Use Planning and Zoning

The key principles to be adopted in land use planning and zoning are thefollowing:

Development and implementation of a zoning plan to separateincompatible and conflicting land uses and the traffic they generate;

Strong planning regulations to influence the location of newdevelopment and to control access arrangements and parking;

Land uses should be planned with the aim of minimizing travel andmaximizing accessibility to public transport;

Residential development should be separated from heavy industry andmajor commercial uses;

Activities which generate substantial traffic should be located adjacentto roads most suited to the type of traffic expected (e.g., if a primaryschool generates many cycle or pedestrian trips, then it should becapable of being reached directly via a network of bikeways orfootpaths); and,

Light industry and service establishments can be located adjacent toresidential areas but vehicular access should not be via the residentialstreets.

Figure 2.1 : Poor Zoning and Road Planning InterfaceFigure 2.1 illustrates a residential area separated from school zone and workplaces by a primary road. Pedestrians crossing the road pose safetyconcerns. A more adequate traffic and land-zoning interface is shown inFigure 2.2 where all developments are located on the same side of theprimary road. This setup then would eliminate safety concerns aspedestrians will not regularly cross the road.




Figure 2.2 : Good Zoning and Road Planning Interface

2.2 Traffic Planning for Different Land Uses

2.2.1 Residential Areas

Residential roads are the prime locations where vehicles and pedestriansinteract and where the movement function fulfills an increasingly minor roleamongst the most important service and domestic activities. In order toprovide a safe environment for vehicles and pedestrians:

Residential roads longer than 100 to 200 meters should be meanderingand should have tight horizontal curves or roundabouts at local roadintersections to encourage low speeds;

Non-access traffic needs to find it impossible, or highly inconvenient, touse residential roads as a short cut;

Pedestrians must be given priority, especially close to buildings and inplay areas;

Direct access to dwellings should be provided from access ways ratherthan distributor roads;

Where dwellings have vehicular access onto distributor roads,

alternative pedestrian access should be provided via segregatedfootpaths onto access ways;

Pedestrians should be segregated wherever possible and crossings oftraffic routes should be convenient and safe;

Parking should be ample and convenient but located away from areaswhere children play;




Drivers need to be made aware of the priority for pedestrians on entryand throughout the area by the overall geometry, surface texture andthreshold treatment as they enter the area;

Large developments should be sub-divided to minimize traffic oninternal roads;

Existing grid networks with cross roads should be modified by closuresor restrictions to create internally or externally-fed systems;

Inter-visibility between drivers and pedestrians should be sufficient tominimize the risk of accidents; and,

Overnight parking of lorries, especially those with hazardous loads,should be actively discouraged.

2.2.2 Industrial Areas

Industrial areas are very important to the economy of most countries and it isnecessary for them to be provided with safe, efficient links to national and

international markets for both raw materials and finished goods. Theimportant factors to consider for the layout and design of industrial estatesare:

Land zoned for industrial purposes should have direct access from thedistrict distributor network whenever possible;

Each site should have sufficient off-road parking and loading areas toaccommodate all its operational, staff and visitor requirements withinthe site boundary;

Roads and footpaths should provide a safe and efficient means ofaccess for workers, visitors and the range of vehicles which can beanticipated when a number of different industries are grouped together;

The internal circulatory system (to at least local distributor standard)should ensure that no traffic queues on the network in normalcircumstances; and,

Networks of safe cycle/footpaths should be created between theindustrial area and the main areas where employees live.

2.2.3 Commercial / Retail Areas

Commercial and retail areas may vary from isolated stalls or street sellers tomajor shopping centers and office developments covering large areas of land.Consequently their transport needs may be very mixed. The main points to

consider in the planning of such areas are: All commercial and trading areas should be away from the through

traffic network. If alongside, then service roads should be provided toservice the development;

Rear servicing, separate from pedestrian access should be providedwhenever possible;

Adequate parking and loading facilities for operational use should beprovided within the site of individual premises if possible;




Visitor and customer parking should be provided off the road, possiblyon a communal basis;

On-street parking should be discouraged and only permitted where itdoes not obstruct general traffic movements or conflict withpedestrians;

Good public transport provision to and within such areas can effectivelyreduce overall parking demand; and,

When rural main roads in developing countries pass through “tradingcenters” it may be necessary to reduce speeds by physical measuressuch as road humps and raised pedestrian crossings to protectpedestrians and shoppers.

2.2.4 Recreational/Tourism Areas

As countries develop, people increasingly find time for leisure andrecreational activities. This leads to demands for sport and recreation centersand leisure parks in addition to major facilities for spectators’ sports. Wheretourist or leisure related activities are encouraged and have become anecessary part of the economy, safe access to them and appropriate parkingfacilities for them may form an important part of their success. The mainconsiderations to bear in mind are:

All recreational generators should be given access from local or districtdistributor roads, depending on their scale;

Recreational land uses should be separated from residential areas, butthey may be on the fringes provided recreational traffic is directedaway from dwellings;

Certain recreational uses may be acceptable within commercial orindustrial areas, although this should be done with care;

Adequate provision of public transport is essential;

All participant and spectator parking (refer to Figure 2.3) should beprovided separately within or near each facility and be sufficient toaccommodate peak demands;

Pedestrian routes between entrances/parking areas and venuesshould be free of vehicular traffic and clearly signposted;

Where events necessitate the use of public highways , they should beclearly segregated from general traffic (periodic closures may be

justified);

Service areas and facilities should be segregated from general trafficand if possible should operate at different times to public use; and,

Certain facilities such as car parks could be shared with other uses.




Figure 2.3 : Ideal Road Network Planning for Tourism Areas




3 ROAD HIERARCHY

Road network is defined as a hierarchy in terms of road types and accordingto the major functions the roads will serve. The main classification is whetherthe road is to be used primarily for movement or for access.

The key points to consider in network planning are the following:

Within the hierarchy, networks should be planned such that areas areseparated into self-contained zones (often referred to asneighborhoods). The size and scale of these zones will depend uponthe importance of the road bounding them. Within these areas all non-essential traffic should be excluded. It should be possible to carry outmost daily trips to shops and schools wholly within the area;

The natural barrier of main routes can be used to segregate andcontain incompatible uses and to reinforce local identities. Thenetwork can be such that traffic can enter zones from an external orinternal system (refer to Figure 3.1). The external system reinforcesthese natural barriers and offers the safest network when well planned.Existing grid-iron networks should be closed off or restricted to createinternally or externally-fed system;

Figure 3.1 : Schematic Hierarchy of Roads




Each class of road should clearly convey to the road user its role in thehierarchy with respect to both traffic volume and design speed. Thiscan be achieved by appearance and related design standards; and,

Each road should intersect only with roads in the same class or oneimmediately above or below it in the hierarchy. In that way, anyoneusing the network has a clear impression of the graduated change inconditions between the low speed access roads and the segregated,higher speed “through routes” at the top of the hierarchy. (refer toFigure 3.2)

Figure 3.2 : Externally and Internally-fed Networks

3.1 Expressways / National Roads

3.1.1 Expressways

An expressway is proposed for a road corridor under the following situations;

A road corridor connecting several highly urbanized centers withribbon-type of development of commercial, business and industrialestablishment.

A road corridor with high traffic demand.

These roads are the longer distance transport routes for motorized traffic.They provide the transportation link between regions and provinces. Theirprimary function is movement and not access.

The elements to consider when planning Expressways are:

No frontage access;




Development set well back from the highway;

Grade separated intersections for extremely high flows and otherintersecting expressways;

Number of intersections to be minimized and

Where necessary or for emergency purposes, parking/stopping to beprovided clear of the main carriageway.

3.1.2 National Roads

National Roads are roads continuous in extent that form part of the main trunkline system; all roads leading to national ports, national seaports, parks orcoast-to-coast roads. National arterial roads are classified into three groupsfrom the viewpoint of function, i.e. North-south backbone, East-West Lateralsand Other Strategic Roads.

The elements to consider when planning National Roads are:

Limited frontage access

Development set well back from the highway;

All access to premises provided via provincial roads;

Number of intersections to be minimized;

Suitable at-grade channelized intersections for minor flows and otherelements

No roadside vendors.

3.2 Provincial Roads

Provincial Roads are roads connecting one municipality with another; allroads extending from a municipality or from a provincial or national roads to apublic wharf or railway station; and any other road to be designated as suchby the Sangguniang Panlalalwigan.

The main elements to consider when planning Provincial Roads include:

Limited frontage access. In exceptional circumstances, large individualdevelopments may have direct access when a high level intersectionis provided;

Development set back from the highway;

Most development to be given access via intersections with localdistributor roads;

All intersections will normally be at-grade;

Turning traffic should be separated out from the through traffic;

Separated pedestrians/bikeways remote from the carriageway;

Pedestrian crossing points should be clearly defined and controlled;




Parking on the road should not be permitted;

Bus stops and other loading areas (only permitted in exceptionalcircumstances) should be in separate well designed lay bys;

Regular stopping places for paratransit vehicles (i.e., private, non-corporately run public transport operating vehicles smaller than buses

or AUV’s) should be identified and safe stopping places established;and,


3.3 City / Municipal Roads

3.3.1 City Roads – these roads / streets within the urban area of the city to bedesignated as such by the Sangguniang Panglungsod.

3.3.2 Municipal Roads – these roads / streets within the poblacion area of amunicipality to be designated as such by the Sangguniang Bayan.

City / Municipal Roads serve to feed traffic onto and off the main road networkat the beginning and end of trips. These roads serve local traffic only.

Main points to consider in planning City/Municipal roads are as follows:

The road is only for local traffic; through traffic is adequatelyaccommodated on an alternative more direct main road;

Where possible, an industrial traffic route should not pass through aresidential area;

Vehicle speeds should be kept low so long straight roads should beavoided;

Parking is allowed, but alternative off-road provision should be made ifpossible;

Non-motorized traffic is of equal importance to motor traffic andseparate route should be provided if possible;

Where non – motorized traffic needs to use a local distributor it shouldbe separated from motorized traffic;

The road width can be varied to provide for parking or to give emphasisto crossing points depending upon traffic flows;

Bus stops and other loading areas (only permitted in exceptionalcircumstances) should be in separate well designed lay bys;

Through-movements should be made awkward and inconvenient todiscourage them; and,





3.4 Barangay Roads

Barangay Roads are rural roads located either outside the urban area of cityor outside industrial, commercial or residential subdivisions which act asfeeder farm-to-market roads, and which are not otherwise classified asnational, provincial, city or municipal roads. Roads located outside the

Poblacion area of municipality and those roads located outside the urbanarea of a city to be designated as such by the Barangay Council concerned.

As the name implies, these roads are for access only and are primarily forresidential uses (industrial access should normally occur from a road of atleast local distributor standard). These are ultimately the streets on whichpeople live. Design standards may vary but the important elements toconsider for barangay roads are:

Vehicle flows to be kept to a minimum;

All through traffic eliminated;

Vehicle speeds to be kept low by careful and deliberate inclusion of

obstructions to create meandering alignments; Access roads kept short where possible;

Cul-de-sac and loop roads to be used wherever possible to deterthrough traffic;

Intersections to be three rather than four leg and kept compact to aidpedestrian movement;

Pedestrian and vehicles can ‘share’ space;

Carriageway width can be reduced to emphasize pedestrian priority;

Entrance/exit points of access streets should be clearly identified bythreshold treatments, e.g. changes in geometric layout, landscaping,building development or even gateways and signing;

Parking and stopping within the streets is permitted although adequateprovision should be provided within individual properties or separategarage areas;

Use of fully mountable curbs for vehicles may enable reduced roadwidth and reduced standard alignments to be used by emergency andservice vehicles, or for occasional parking; and,

Firepaths (emergency accesses for the engines) can be kept clear byusing diagonal closures to eliminate parking spaces or by ensuring

other nearby owners gain access by the same route so that they keepthem clear.




Figure 3.3 : Road Network that Attracts Through Traffic Onto Local Roads

Figure 3.4 : Road Network that Deters Through Traffic from Using Local Road




Figure 3.5 : Road Layouts that Deters Through Traffic from Using Local Roads

3.5 Pedestrianized Areas/Routes

These are areas from which all motorized vehicles are excluded to improvesafety. In their broadest sense they would include all routes where non-motorized traffic has sole priority. This would include purpose-built footpathsand bikeways that often form a totally separate network to that for motorizedtraffic in residential areas. In planning new pedestrian networks and areasthe key points to consider are:

Residential, industrial and commercial areas should be linked byfootpaths providing the most direct and pleasant route betweendestinations.

Any deviation from a direct route should be more attractive than a lesssafe option;

All crossings with main routes should be grade separated whereverpossible and if not possible additional at-grade facilities (e.g. refuges orpedestrian crossings) should be provided to minimize crossingproblems;

Vertical rerouting (via over bridge or underpass) is much less attractiveto pedestrians than at grade facilities;

The vertical and horizontal alignments of pedestrian routes can includemuch steeper gradients and sharper bends than for a roadway formotor traffic;

Open aspects need to be maintained, particularly at intersections andunderpasses;

In shopping and commercial areas priority needs to be given topedestrians;




Where motor vehicles are displaced, adequate capacity (for loading,parking and movement) needs to be available elsewhere on thesurrounding roads but such facilities should always be within easywalking distance;

If no alternative provision can be made for motor traffic, considerationmay be given to pedestrianization by time of day i.e., vehicle accessallowed only when pedestrian flows are light (e.g. very early in themorning or late at night);

Connections to bus stops, parking areas and stations are vital andshould be convenient; and,

All pedestrianized areas must have provision for access of emergencyvehicles and refuse collecting vehicles.




4 ROUTE PLANNING THROUGH EXISTING COMMUNITIES

Bypasses around communities are countermeasures aimed at improvingsafety and reducing the volume of through traffic inside the community. In thePhilippines, this is a common practice particularly around the countryside.However, building bypasses is just an alternative countermeasure ofdiscouraging traffic to pass within the community. Other countermeasurescan be devised depending on economic and budgetary constraints.

Where a bypass can be justified, the most important considerations are:

The opportunity should be taken to reinforce the road hierarchy bydown-grading the old road to discourage through traffic;

Access to the bypass should be restricted to only a few points wheresafe intersections and spur roads can be provided to link to the existingnetwork. Direct access from frontage land should not be permitted;and,

Provisions should be left for future expansion or development of thecommunity but such developments should be served by service roadsand spur roads.

Where a bypass cannot be justified, countermeasures should be implementedto slow down the speeds of through traffic as it passes through the communityor trading centers as follows:

Warning signs and rumble strips can be used to alert drivers aboutspeed-reducing devices ahead;

A series of road humps increasing in height from 40mm to around80mm can be used gradually to slow down traffic in pedestrian

predominated areas; Road narrowing (with due regard for capacity needs) can be used to

induce lower speeds as traffic passes through the community; and,

In order to alert drivers that they are entering a community, it isgenerally regarded that some form of gateway treatment on theapproaches is beneficial (e.g., substandard curve, tree lining, or evennon-rigid gate structure).




Figure 4.1 : Road Layout that Results in Conflict Between Localand Through Traffic

Figure 4.2 : By Pass Road Deters Through Traffic from theCommunity




5 DEVELOPMENT CONTROL / ENCROACHMENT

Planning is a constantly changing process. The difficulty is to control thedegree of change so that the various inter-related elements can still operateefficiently. In land use terms this is usually achieved (with varying degrees ofsuccess) through the control of existing or new development and preventionof uncontrolled parking, illegal accesses and spread of unauthorizedcommercial activity. The main points to consider are that:

Strict control of roadside hoardings and advertisement boards isrequired;

Land–use and highway requirements change over time so some sparecapacity should be designed into road networks to enable suchchanges to be accommodated without detrimental effects upon roadsafety;

Building regulations should include ‘building line’ specifications tocontrol roadside development;

If development control standards permit the growth of activities toencroach onto the transport corridor, additional countermeasures maybe required to maintain a safe level of service to the community as awhole;

Strong development control can only prevent encroachment onto roadsif there are alternative locations for commercial activities to beundertaken; and,

Unauthorized development such as roadside advertising boards, illegalaccesses and market stalls which create unsafe traffic conditionsshould be removed as soon as possible and the sites monitored toprevent their reappearance.

source: US Highway Capacity Manual

Figure 5.1 : Encroachment that Reduces Effective Sidewalk Width




6 ACCESS CONTROL

Access control applies to both vehicular and pedestrian traffic. Localpractices have shown different practices in treating access to developmentssuch as:

Provision of elevated pedestrian walkways or underpasses to separatepeople from road traffic. Oftentimes, these facilities have direct accessto respective developments such as shown in Figures 6.1 and 6.2.This strategy does not only improve safety but also enhancecommercial attractiveness of an establishment to its target market.

Driveways should not lead directly to a high speed road facility as thismay create conflict and compromise safety. Good management ofaccess to roadside properties on arterial roads can reduce conflictbetween through traffic and local traffic, for example by the provision ofservice roads.

Large parking facilities should locate entrance/exits away from high-speed roads, but with good access circulation leading to high speedroads;

Expressway ramps should be carefully planned to reduce conflict withlocal vehicle and pedestrian traffic;

On new roads of district distributor level or higher, direct frontageaccess should only be permitted in exceptional circumstances;

The number of direct accesses onto main roads should be minimizedand service roads or collector roads used to bring traffic to a single T-

junction at the main road;

No access should be permitted at potentially dangerous locations (e.g.,at road intersections, or on bends with poor visibility); and,

In all cases, each class of road should intersect only with roads in thesame class or one immediately above or below it in the hierarchy.




source: DPWH / MMURTRIP

Figure 6.1 : Walkways and Overpass to Control Pedestrian Access


Figure 6.2 : Service Road and Segregated Walkway to Control Local Traffic Access




7 TRAFFIC IMPACT ASSESSMENT (TIA)

Recent developments in transportation research in the Philippines haveresulted in the formulation of a TIA Handbook. This handbook was preparedby the National Center for Transportation Studies (NCTS) in order tostandardize the conduct of TIA. In addition, it is worth giving more emphasison road safety as well as the traditional subjects such as volume control,traffic forecasts, demand management, and congestion mitigation.

Some interesting subjects for consideration in the TIA is the interfacebetween land use development and traffic, and this should be reviewedagainst the guidelines of the Housing and Land Use Regulatory Board(HLURB). Parking demand and restrictions should also be strictly followed asmandated by the National Building Code. Preferably, parking demand shouldbe based on local parking indices and not on international practices sincelocal traffic conditions very much differ from other countries’ experiences.Pedestrian considerations should also be given more weight in the planningstage.

Road safety is given importance in the proposed TIA guidelines. The generalscope of works on the proposed guidelines cover the following:

Transportation Improvement

Road Geometry

Traffic Safety

Site Circulation and Parking

Transportation facilities related to public transport, bicycle, andpedestrian travel

Transportation demand management

Neighborhood traffic and parking management

Funding for countermeasures

Likewise, the NCTS TIA guidelines have listed the standards of significancefor traffic impacts of a project:

If the projected traffic will cause the existing intersection or highwayroadway levels of service to drop below an acceptable level of service;

If the projected traffic will contribute to the increase in traffic alongarterials or at intersections currently operating at unacceptable levels.

If the project design does not have adequate parking or circulationcapacity to accommodate an increase in traffic.

If the traffic increase or roadway design will result in safety concerns;or,

If the project does not include adequate provision for bicycle,pedestrian, or public transport access.




8 ROAD DESIGN PARAMETERS

8.1 Speed Management

8.1.1 Design SpeedThe choice of an appropriate design speed for a road project is important toensure a safe design.

When choosing a design speed , the following factors need to be considered:

Function of the road. An arterial road such as a national highwaywould generally have a higher design speed than a local road.

Anticipated operating speed. For example, a national highway in anarea with steep terrain would generally have a lower design speed (i.e.smaller radius curves) than a national highway in flat terrain wherehigher speeds would generally be anticipated and hence large radius

curves adopted. In these examples the anticipated operating speed ofthe new facility (that may include improved alignment and roadsurface), should form the basis for determining an appropriate designspeed, rather than the operating speed of the existing road.

Anticipated speed limit. When considering the design speed along aroute , it may also be necessary to adopt a different design speed fordifferent sections of the road as circumstances change . For examplewithin a town or on the road section between towns.

Economics. The implications relating to cost of construction.

8.1.2 Speed Implications

Research shows that lower speeds lead to fewer and less serious crashes.There are two reasons for this:

At higher speeds a rider or driver has less time to react to a situationand therefore there is a greater likelihood that an error will result in acrash; and,

The momentum and kinetic energy of a vehicle increases rapidly withspeed. The sudden dissipation of this energy in a crash means thatthe injury to occupants is more severe.

Therefore , a carefully planned speed limit regime can make a significantcontribution to road safety.

8.1.3 Current Speed Limits

The current speed restrictions are set out in Chapter IV – Traffic Rules, inRepublic Act No. 4136 ‘Land Transportation and Traffic Code.’

The rules indicate that a motorist shall drive at a safe speed determined bythe driver based on the road environment and conditions. There are howevermaximum allowable speeds for different road environments.




On open country roads with no “blind corners” not closely bordered byhabitation, the maximum speed for passenger cars and motorcycles is 80kphand for motor trucks and buses, 50kph.

On “through streets” or boulevards clear of traffic, with no “blind corners”,when so designated, the maximum speed for passenger cars andmotorcycles is 40kph and for motor trucks and buses, 30kph.

On city and municipal streets, with light traffic, when not designated “throughstreets”, the maximum speed for passenger cars, motorcycles, motor trucksand buses is 30kph.

Through crowded streets, approaching intersections at “blind corners”,passing school zones, passing other vehicles which are stationary, or forsimilar dangerous circumstances, the maximum speed for passenger cars,motorcycles, motor trucks and buses is 20kph.

Where it is determined that a road should have a different speed restriction tothat indicated above, then specific speed restriction signs should be installedto inform motorists. The following sections describe where certain speedrestrictions could be appropriate.

High Risk Pedestrian Areas – 40 kph

Vulnerable road users, especially pedestrians, are particularly vulnerable athigher speeds. The graph below based on international research shows therisk of a pedestrian fatality if hit by a vehicle at different speeds.

Figure 8.1 : Risk of Pedestrian Fatality

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 Impact Speed (km/h)

R i s k o

f F a

t a l i t y ( % )




For instance 25% of people struck by a vehicle traveling at 40 kph wouldsuffer fatal injuries. At 50 kph this risk increases to 85%. Therefore a speedlimit of 40 kph or lower would be appropriate in areas where there is highpedestrian activity such as in city center areas.

A 40 kph speed limit would also be appropriate on roads where there are nofootpaths and pedestrians are required to walk on the road.

Low risk pedestrian areas – 60 kph

On roads through built-up areas where there are not so many pedestrians, itis appropriate to allow motorized traffic to travel more quickly.

The following picture shows the type of environment where 60 kph may beappropriate. Although this road is carrying vulnerable road users, they have aseparate lane to travel in.

Figure 8.2 : High Speed Road with Separate Lane for Non-Motorized Vehicles

80 kph

An 80kph speed limit would be appropriate on a high standard duplicatedcarriageway road where there is only occasional access from adjoiningproperties.

100 kph

A 100 kph speed limit would only be appropriate on very high standardexpressways, which have a low crash rate. These expressways should havea high standard geometry and should be free of roadside hazards. If hazardsexist and they cannot be removed or modified, they should be shielded with asafety barrier.




8.1.4 Speed Restriction Signs

Good speed management practice depends on speed limit signs being placedin visible locations and repeated frequently enough for motorists to be certainof which speed zone they are in.

At the start of a new speed zone , a speed limit sign should be erected on theleft and right sides of the road. Then within the first kilometer, there should betwo (2) farther pairs of repeater speed limit signs. After that, repeater signsshould be placed at one kilometer spacing.

Repeater signs should also be placed before and after all major intersectionsto confirm the speed limit to all traffic turning into the road being considered.

8.1.5 Poor Road Standards

If the standard of the road geometry or its surface is poor, then it may beappropriate to adopt a lower speed limit than would normally apply until suchtime that the road improvements can be made. The lower speedscompensate for the hazardous conditions of the road.

An 80kph or 90kph speed limit may also be appropriate on lower standardexpressways. For instance , the concrete plant cylinders on the side of theexpressway as shown in Figure 8.3 are a serious road hazard within the clearzone which could cause injury to the occupants of an out of control vehicle. Ifthis roadside hazard cannot be removed or protection for vehicles provided,the speed limit should be restricted to reduce the risk to motorists and riders.

Figure 8.3 : High Speed Road with Wide Median

8.2 Road Capacity

Road Capacity, as defined in the U.S. Highway Capacity Manual (HCM), isthe maximum number of vehicles, which have a reasonable expectation ofpassing over a given section of a lane or a roadway in one direction or in bothdirections during one hour under prevailing road and traffic conditions.




Generally, road capacity with respect to road sections is measured in terms oflevel-of-service. This is designated with letters ‘A’ to ‘F’ with ‘A’ the most idealcondition and ‘F’ the saturated condition where volume is equal to the roadcapacity.

In regard to intersections, capacity is generally measured in terms of ‘degreeof saturation.’

The capacity of a route can be affected by the following factors:

Number of Lanes;

Lane and shoulder width;

Terrain and road gradient;

Traffic composition;

Side friction such as the presence of road furniture and pedestrians;and

Intersection capacity (priority of movements, traffic signal phasing,number of lanes etc.).

Ideal capacity of a road is 2,000 vehicles/hour (vph). However, based onseveral surveys conducted in Metro Manila for various infrastructure projects,it was found that the maximum volume is achieved only at a level of 1,400vphon expressways and 1,100 for urban arterials.

In the design stage of a road project, appropriate capacity should beestablished to ensure satisfactory operation. In establishing the capacity ofthe road , actual traffic surveys as well as investigation of future use isrequired to ensure that safety is not compromised once the facility is inoperation.

8.3 Traffic Forecasts

Experiences in the Philippines indicated that traffic forecasts for expressways(tolled facilities) are usually optimistic. This may be seen as a factor to boostrevenue forecasts to make the road appear more interesting to investors.The opposite can be true in planning urban arterials as forecasts are oftenbelow actual traffic counts once the facility is in operation. The latter hasmore impact on traffic safety since it could mean more traffic is using the roadthan the volume for which it was originally designed. Further, roadmaintenance is often compromised when traffic exceeds the forecasts (e.g.thickness of pavement, lane width, maintenance budget, etc.).




9 PUBLIC TRANSPORT

Public transport refers to public utility jeepneys, buses and taxis.

9.1 Public Transport Operations

The rule of thumb to enhance safety in the operations of public transport as inthe case of Metro Manila is to segregate them from private cars. Theprovision of “yellow lanes” on some major thoroughfares of Metro Manila isseen as good practice. However, proper planning should be conducted onlocating loading and unloading areas for passengers. Theseloading/unloading areas should be located in vicinities that offer protection tocommuters and pedestrians.

9.2 Lay-bys, Bus Stops and Service Roads

Lay-bys and bus stops allow public transport vehicles to stop safely and withthe minimum of adverse effects on other traffic. This is best done with asegregated area joined to the main road pavement only at an entry point andexit point. Vehicles can then stop off the main carriageway without interferingwith other traffic and with less risk to passengers getting on or off.

Where primary roads are bordered by commercial or residential development,service roads are the safest way of allowing access to property with theminimum effect on other traffic. Also, where a large commercial developmentis fronted by an informal parking area with controlled access to thecarriageway, a significant risk of accidents will often exist.

The general guidelines in planning for public transport facilities are as follows:

Lay-bys should be positioned on straight, level sections of road andshould be visible from a good distance in both directions.

On rural roads, it is cheaper to provide lay-bys at transitions from cut tofill.

Access to lay-bys should be convenient and safe for vehicles and alsofor pedestrians in the case of bus stops.

Advance warning signs could be erected to alert drivers of theapproach to lay-bys, and to the possible presence of pedestriansahead.

Adequate queuing and waiting areas should be available so that

waiting passengers do not use the road or a dedicated bus lay-by. Where space is limited, it may be possible to link premises using a

service road, which runs behind the premises and turns to rejoin themain road only when a convenient and safe location is reached. At thispoint, parking and other potential visual obstructions should becarefully controlled.




Where problems of merging from a lay-by occurs, it may be possible topostpone the merge by providing a short additional lane, which is thecontinuation of the lay-by.

Where spillage of diesel fuel is likely to occur, e.g. at bus stop,concrete construction is more suitable than a bituminous surfacing.(Buses will not use the stops if the road surface has deteriorated.)

Bus stops should be located beyond pedestrian crossings and afterintersections to avoid stopped vehicles masking pedestrian and othercrossing activities.

Source: DPWH / MMURTRIP

Figure 9.1 : Bus Stop Concept, EDSA

Source: DPWH / MMURTRIP

Figure 9.2 : Lay-By Concept, EDSA




On highly trafficked or arterial roads , it is desirable for public transportvehicles to stop off the main carriageway. In urban areas, it can beadvantageous to locate indented bus or jeepney stops on the downstreamside of major signalized intersections. This can improve the ability and safetyof the vehicle to re-enter the traffic stream. The guidelines in the design andlocation of turn-outs along national road shall conform to D.O. No. 58 seriesof 2010.




10 VULNERABLE ROAD USERS

Vulnerable road users include:

Pedestrians

People with disabilities

Non-motorized vehicles

Motorcycles

10.1 Pedestrians

Motorized vehicles are not the only means of transport using the road system.Other road users such as pedestrians and cyclists need to be catered foradequately so that they can use the road space safely.

The safest way to cater for these groups is to provide separate areas for them

to use.

Figure 10.1 : Poor facilities for pedestrians

Figure 10.1 shows a location where pedestrians need to share road spacewith vehicles as there is no shoulder or sidewalk. In some situations,consultation may be required with the Local Government Units (LGUs) tocontrol the use of roadside areas.




Pedestrians are separated from fast-moving traffic

The open drain has been covered to provide a sidewalk.

Figure 10.2 : Good Pedestrian Facilities




Figure 10.3 : Obstructions that Reduce Effective Travel Width for Pedestrians

At intersections, it is important that pedestrians have somewhere safe to wait,which is separate from the roadway.

At unsignalized intersections, pedestrians can be catered for by use of apedestrian crossing marked on the roadway. It is important that this issituated as close to the intersection as possible so the pedestrian is visible tothe motorist.

10.2 Cyclists

It is desirable that separate lanes be provided for cyclists, especially on

heavily trafficked routes. Cyclists are unprotected and when mixed with fastermoving vehicles can produce a hazardous situation.


Figure 10.4 : Segregated Pedestrian and Bikeway from Main Thoroughfare




Figure 10.5 : Road without bike lanes




11 PARKING

The effective control of parking and appropriate provision of parking facilitiesis required to maximize safety and to limit impacts on traffic flow.

Expressways. Generally, parking is not appropriate along expressways andthese roads need to have signs that inform drivers of the parking restriction.

National Roads. Parking should not be permitted along national roads.

Local Roads. Parking bans are generally not appropriate, however, the timesand duration of parking may need to be indicated on signs.

Subject to the consideration of safety and traffic flow needs, where parking isto be permitted within certain areas along roadways, consultation and co-operation between agencies is desirable to ensure that proposals areappropriate.

11.1 Parking Near Intersections

Vehicles parked near intersections can obstruct the flow of turning traffic.Thus, parking should be prohibited within the following minimum distancesfrom the boundaries of intersecting roads:

Parallel parking – 6m on both approach and exit sides

Angle parking – 12m on approach side, 9m on exit side

It is desirable that on the approach side of a signalized intersection, parkingbe prohibited for a distance large enough to store as many vehicles as cancross the stop line in one phase from the curb lane.

11.2 Angle Parking

All forms of angle parking present a greater hazard than parallel parking.Therefore the function of the road needs to be considered relating toproposals for angle parking on or adjacent to roads.

Generally, the use of angle parking shall be:

Expressways - No provision except for off-road roadside stoppingareas.

National Road- Parking and maneuvering associated with angle

parking to be executed completely clear of through traffic lanes. Aphysical separation in the form of an outer separator should be madebetween the parking-maneuvering area and the through traffic lanes.

Provincial Roads - Angle parking on these roads may be appropriate.However, it is preferable that the marked parking bays andmaneuvering area are physically protected with a curb extension.




Figure 11.1 : Angle Parking with Maneuvering Area Clear of Through Traffic

Lanes Municipal/City Road - The maneuvering of vehicles for parking may

encroach into the through traffic lanes on that side of the center line. Itis also desirable that the marked bays should be physically protectedas discussed for secondary arterial roads.

Local Roads - The maneuvering of vehicles for parking may encroachonto both traffic lanes where traffic volumes are low and the level ofdelay or congestion can be accommodated.

The following guidelines should be observed for angle parking:

The words “Angle Parking” shall be indicated on the parking signs as

well as the angle of parking to the curb;

Pavement marking of parking bays is desirable, particularly where therequired angle is not 45 or 90 degrees; and

Angle parking shall not be installed where visibility restrictions wouldcreate a hazardous operating environment, such as the inside of abend or on a crest.

11.3 Parking Adjacent To Barrier Lines

When considering parking adjacent to barrier lines the following factors

should be considered: If parking maneuvers can be made clear of through lanes. Generally,

at least 3 meters needs to be available for moving traffic between theparked vehicle and the barrier line for a single lane of traffic.

The loss of capacity during parking maneuvers if the maneuvers arenot completely clear of through lanes.




The safety and potential of vehicles crossing the barrier line to pass avehicle in a parking or unparking maneuver even though this is anunlawful maneuver.




12 LIGHTING

The introduction of adequate street lighting can help reduce nighttimeaccidents and is an established accident prevention measure in urban areas.It is particularly important where there are high proportions of pedestrians,cyclists or other poorly lit road users, including animals. Lighting has benefitsother than accident prevention and can often be justified as a general amenitywith an associated reduction in nighttime crime and an improvement inpersonal security.

Generally , there is a need to improve street lighting especially where thereare high pedestrian flows. The most important aspects to consider are:

Evenness and type of illumination is important (refer Figure 12.1). Thisrequires good design and regular maintenance. A routine maintenanceprogram should be initiated and all installations inspected on a regularbasis;

Light poles should be sited in positions where they will not be a dangerto a vehicle leaving the road or designed as frangible poles (slip-basepoles or impact absorbent poles) that slip away or collapse on impact.In other situations , a safety barrier may need to be provided to protectoccupants of an errant vehicle.

Signs and road markings should be visible at night. Where lighting isnot feasible, use of reflective material is a useful, cheaper alternative;

Lighting is most important at key locations such as at sub-standarddesign sections, at sites where the layout may be unclear, atintersections, and where pedestrians cross; and,

Consideration should be given to the use of high pressure sodium ormetal halide lighting, particularly at key points, as it is much more

efficient than mercury or tungsten lighting.

It is important that intersections are adequately lit as it is in this area wherevehicles of different speeds can interact. Vehicles are slowing down in thisarea to make a turn or enter an intersecting road. At intersections it isimportant to ensure that elements such as raised islands are adequately lit asthese provide the motorist with early indication of the intersection. Figure12.2 shows typical locations for street lighting at intersections.

For route lighting on duplicated roads, frangible lighting poles shouldgenerally be located centrally in the median with lights on cantileveredbrackets over the roadways. On undivided roads lighting poles would belocated alternately each side of the roadway. The spacing of lighting poles

along the route is subject to the wattage and mounting height of the lightschosen.

A uniformly lit surface should be provided and therefore maintenance isimportant. Inconsistent lighting can itself be a hazard. Lighting is especiallyimportant where large numbers of pedestrians or cyclists are expected.

Further information regarding frangible poles is in Section 20.6.7 andAppendix 3.




Different Types of Lighting

Before (streetlight using ordinary mercury andhalogen lamps)

After (streetlight using metal halide lamps)

Effect of Over Illumination on Streets

Before (Over illumination causes glare) After (Adequate lighting improves visibility)

Proper luminance and lighting

Before (Dimly lit using mercury lamps) After (Adequate lighting using metal halide)

Figure 12.1 : Types of Lighting and Illumination




Figure 12.2 : Lighting Installations at Intersections

Cross Road Intersection

Roundabout Intersection

S is the design spacing of lamp posts for major roads

T--Intersection

w x E∅ x Cu x mf

where :

S = spacing of lamp postw = width of the road

E = Illumination in Lux∅ = lamp lumenCu = coefficient of utilizationmf = maintenance factor

S =




SAFETY DESIGN




13 INTRODUCTION

13.1 Background

This section of the manual describes how the road network can be made tobe safer through the awareness of safety principles during the design stages.

13.2 Safe Design Principles

The first aim of safe road design is to ensure that road users remain safely onthe road. This depends on the following factors:

a sound road surface;

an adequate width or cross-section;

horizontal and vertical alignment;

good visibility/sight distance;

delineation and signing;

provision for pedestrians, pedal cyclists and people with disabilities;

management of traffic conflicts at intersections; and,

speed management.

However, drivers and riders will sometimes make mistakes and lose controland leave the road. At that stage it is important to provide a forgivingroadside.




The road edge can also cause problems for vehicle safety.

Figure 14.2 : Poor Road Edge

Figure 14.2 shows the edge of a road with a level difference on the adjacentshoulder. If a driver lost partial control of a vehicle on this curve and a wheelwent over the edge of the road, it could be difficult for the driver to regaincontrol due to the large drop off at the road edge. The driver could then losetotal control and run into a roadside hazard such as the pole in thephotograph.

The objective of providing an even, well drained and good textured road

surface is aimed at keeping traffic safely on the road. Maintenance of theroad surface is also essential to maximize safety and prevent traffic accidentsoccurring.




15 ROAD ALIGNMENT CONSIDERATIONS

15.1 Introduction

In many design situations, designers will be faced with competing demandsfrom different sections of the community as they endeavor to design safe,operationally efficient roads. The horizontal and vertical alignment and thecross section of a road should be designed so that a driver or rider can travelsafely at an appropriate operating speed and have adequate sight distance ofthe road ahead. If constraints require a tighter alignment, then it is imperativethat the driver or rider be provided with the necessary visual and physicalfeatures to enable the driver to perceive the changed conditions accuratelyand to select an appropriate lower speed.

For details relating to road alignment refer to Section 16 of this manual andDPWH Highway Design Guidelines Chapter 3.

15.2 Some Physical Problems

Problems arise if the alignmentchanges suddenly and unexpectedly.

A horizontal curve over a shortvertical crest is shown in Figure 15.1.The three photographs show thedrivers view as the crest isapproached. The sequence ofpictures shows that the curve is notvisible until the driver can see overthe crest.

Although this road has a centerline itdoes not give the motorist sufficientadvance warning that the road willchange direction. Some chevronhazard signs may improve delineationin this situation.

However, in new design situations thecurve should be commenced beforethe crest to ensure the curve is visibleto drivers. This would improve safetyand may avoid the need to useadditional signs.

Figure 15.1 : Poor Design andDelineation of Curve




Figure 15.2 : Lost Control on Curve

A horizontal curve at the end of a steep downgrade can mislead a driver orrider and they can find themselves approaching the horizontal curve tooquickly. This can lead to loss of control of the vehicle and the possibility thatthe vehicle could run off the road and collide with a roadside hazard.

Figure 15.3 : Extreme topography results in small radius curves

The road alignment in Figure 15.3 changes quickly due to the extremetopographical terrain resulting in a number of small radius curves. At night,particularly with the headlight glare of an oncoming vehicle, it would be verydifficult to visualize the road alignment. A centerline and edge line pavementmarkings would assist the motorists considerably. Strategically placed curvemarkers and guideposts would also help.




Figure 15.4 : Trees Obstructing Sight Distance

Trees or vegetation as shown in Figure 15.4 can often hide the roadalignment. During daytime, dangerous corner cutting will be encouragedbecause the pavement markings are not adequate. If the vegetation cannotbe trimmed, the alignment would be improved by providing strategicallyplaced chevron signs or guideposts. The centerline markings should bebarrier lines where visibility is poor.

Figure 15.5 : Poor Vertical Alignment Approaching a T-Intersection

Poor vertical alignment through an intersection can obscure the layout of anintersection. For example in Figure 15.5, it is not possible to see theintersecting cross road surface. This could cause vehicles to stop in thewrong place, for instance in the path of cross traffic.




Figure 15.6 : Poor Intersection due to Lack of Channelization

Lack of channelization in Figure 15.6, leads to poor driver behavior such ascorner cutting or lane blocking. If vehicle movement is unpredictable acollision is more likely to occur. Installing a centerline, edge-line marking anda stop or holding line would improve the intersection considerably. If anintersection like this one had a poor accident record, then a splitter islandcould be considered to give a clear indication of alignment and where thedriver should stop.

This would be an ideal location for a small radius roundabout. This wouldimprove safety as well as improving traffic flow to become orderly andpredictable. Figure 15.7 shows a small radius (5m radius) roundaboutoperating very well in Balayan town, Batangas.

Figure 15.7 : Small (5m radius) Roundabout in Balayan Town




Figure 15.8 : Horizontal Curve at the End of a Steep Downgrade

It is difficult to determine the nature of the horizontal curvature at the end ofthe steep grade due to poor sight distance. The motorist may approach tooquickly and lose control. Improved sight distance could be achieved by cuttingback vegetation by providing a sight bench. A centerline, guideposts andchevron road signs would also improve awareness.

Figure 15.9 : Poor Vertical Sag

The short vertical sag curve in Figure 15.9 can hide a vehicle. Motorists maytry to overtake thinking the road ahead is clear without realizing that a vehicleis hidden from view in the sag.

A good treatment would be to delineate the road with no overtaking lanemarkings. Lane widening over the short crest would provide extra width formaneuvering vehicles.




Figure 15.10 : Reverse Curves

Closely spaced reverse curves as in Figure 15.10 have a short straightbetween the two curves. Closely spaced reverse curves without a length ofstraight alignment between the two curves is undesirable as the standard rateof change of cross-fall (super-elevation) is always exceeded. This can lead toloss of vehicle control when the road is wet. It is also very hard for themotorists to determine the road alignment in advance. It is desirable to havethe length of the tangent between reverse curves not less than 50m.In nocase shall the tangent length be less than 30m. Centerline and lane markingsshould be provided as well as chevron signs.

Figure 15.11 : Poor Combination of Horizontal and Vertical Alignment

A poor combination of horizontal and vertical alignment is shown in Figure15.11. The poor alignment is coupled with a structure at the lowest section ofthe vertical alignment. Notice the small vertical curves provided at theapproaches to the structure to keep the structure on a level position.




Traffic coming from both directions cannot pass this section of the road at thesame time due to the acceleration needed by the vehicle to negotiate thesteep gradient in both directions.

Provision of a Give Way sign on one approach and information signs on bothapproaches of the bridge would help motorists to traverse this section of road.This would provide the traffic management needed to control vehicles in thecourse of traversing this section of road. It is a situation that should not beprovided in a new road design.

Figure 15.12 : Delineation of Curve – Poor night-time visibility

The raised, colored, back to back curb, form of curve delineation in Figure15.12, is intended to discourage vehicles moving into the opposing lane.While this may be effective during daylight hours, this median treatmentwould not be very visible at night. Also, if a driver inadvertently struck theraised island this could cause the driver to lose control. The best way to treata ‘substandard’ or unexpected curve is to provide barrier lines withreflectorized pavement studs (RPS), edge lines and chevron hazard signs orguide posts. If a curve is experiencing a number of loss of control crashes,then it may be appropriate to provide these devices.

Other aspects that could contribute to loss of control on curves are:

Adverse superelevation;

Poor sight distance; and

Poor surface condition.

Other types of improvements that could be considered are:

Curve radius improvement; and

Pavement widening.




16 ROAD ALIGNMENT GEOMETRY

16.1 General

The geometric detail of alignment design is an essential ingredient toachieving a safe road. The alignment parameters are generally based on thechosen design speed for the length of road being designed. Each section ofthe road making up the length of road is then analyzed against the roadsafety design criteria appropriate for the section form and geometric detail.

Safe road design needs to consider the following design features:

• Design speed (kph);• Sight distance (m), Stopping Sight Distance - SSD (m);• Straight section length - tangent – T (m);• Radius of circle curvature - R (m);• Circular curve section length - Lc (m);• Spiral section length (Clothoid – Ls (m);• Normal cross slope - Nc (%);• Design superelevation - e (%);• Superelevation runoff length - Sro (m), from zero cross slope to design

superelevation;• Portion of superelevation runoff - Psro (m) prior to the tangent to the

circular curve (PC);• Length of spiral equals the length of superelevation runoff

Ls = Sro;• Tangent runout length - Tro (m), zero cross slope to normal cross

slope;• Length of superelevation development (Le)

Le = Sro + Tro;• Grades of positive or negative longitudinal slope ( + %);• Vertical curves either crest or sag - L (m);• Algebraic grade change - A ±±±± (%);• Rate of vertical curvature - K (m) = L (m)/A (%);• Cross section:

o Traveled way, traffic lane width and slope - w (m and %);o Shoulder width and slope (m and %);o Fore slope and back slope (m and %);o Median width (m);o Sidewalks;o Curbs: barrier curb or mountable / drop curb;

• Drainage channels;• Utility poles;• Frangible lighting poles - impact absorbing poles and slip-base poles;

L(m)± A(%)




• Road safety barriers: roadside, median and crash cushions;• Frontage roads;• Overtaking lanes, climbing lanes and turnouts - w (m).

16.2 Design Standards

The general design standards for the Philippine National Highways are shownin Table 16.1.

The design speed for flat and rolling terrain should be high to meet theexpectations of drivers. There is a definite safety concern if lower designspeeds are used for low volume roads in flat or rolling terrain as drivers willdrive at higher speeds. There will then be inadequate sight distance anddesign appropriate for the travel speeds. There is good logic in using designspeeds appropriate to the terrain being traversed rather than traffic volume.This is recognized in the Table 16.1 for mountainous road design speeds.

The standards for curve radii and grades are shown as minimum radii andmaximum grades. The choice of smaller radii and steeper grades beyond thestandards need to be approved by the Bureau of Design Director to maintaincontrol on otherwise sound standards.

Geometric standards are important criteria for road safety and the maximumvalues are shown in table 16.1.



May 2004 Road Safety Design Manual

(For BOD final review) Table 16.1 : Design Standards for Philippine National Highways

ADT (Average Daily Traffic) Under 200 200 - 400 400 - 1000 1000 - 2000 Minimum Minimum Minimum Desirable Minimum Desir

DESIGN SPEED (kph)Flat Topography 60 70 70 90 80 95

Rolling Topography 40 50 60 80 60 80 Mountainous Topography 30 40 40 50 50 60

RADIUS (meter)Flat Topography 130 175 175 400 260 400 Rolling Topography 50 80 130 260 130 260 Mountainous Topography 30 50 50 80 80 130

GRADE (%)Flat Topography 6.0 6.0 5.0 3.0 4.0 3.0 Rolling Topography 8.0 7.0 6.0 5.0 5.0 5.0 Mountainous Topography 10.0 9.0 8.0 6.0 7.0 6.0

CROSS SECTION (meter)Traffic Lane Width (m) 1 x 4.0 / 4.0 2 x 3.05/ 6.10 2 x 3.35 / 6.70 2 x 3.35 /6.70 2 x 3.35 /6.70 Shoulder Width (m) 0.5 1.0 1.5 2.0 2.5 2.5 (

Right Of Way Width (m) 20 30 30 30

STOPPING (NON – PASSING) SIGHT DISTANCE (meter)Flat Topography 85 105 105 160 130 175 Rolling Topography 50 65 85 130 85 130 Mountainous Topography 35 50 50 65 65 85

SAFE PASSING SIGHT DISTANCE (meter) Flat Topography 410 485 485 615 540 645 Rolling Topography 270 345 410 540 410 540 Mountainous Topography 200 270 270 345 345 410

SURFACE TYPE

Gravel, Crushed Gravel or Stone,Bituminous Preservative Treat.

Single or Double Bit. Treatment,Bituminous Macadam Pavement

Bituminous Macadam Pavement,Dense or Open Graded Plant Mix,Bit. Concrete Surface Course,Portland Cement Concrete

Bituminous Concrete SurfaCoursePortland Cement ConcretePavement

Source: AASHTO, A Policy on Geometric Design of Highways and Streets, 2001




16.3 Sight Distance

16.3.1 Introduction

The drivers ability to see the road ahead is of utmost importance in thesafe and efficient operation of a vehicle on a highway. This sightdistance needs to allow the driver time to perceive and react to anyhazardous situation. It needs to enable the driver to avoid any object orcome to a safe stop before colliding with the object or vehicle.Adequate sight distance should be provided in both the horizontal andvertical directions. Clear signing and pavement marking systemsshould be provided to indicate locations where the sight distance isinadequate for safe overtaking.

The provision of safety sight distance depends on the characteristics ofthe driver, the vehicle and the environment:

Driver

Alertness of driver

Recognition of the hazard

Actions available to the driver – to stop or to change direction

Vehicle

Type of vehicle – car or truck

Friction between the tire and the road

Eye height of the driver

Speed of vehicles

Road Environment

Road geometry – grade and curvature sight limitations

Road surface – sealed or unsealed, smooth or rough

Road illumination at night

16.3.2 Sight Distance Elements

Each type of sight distance consists of three elements:

Driver Eye Height is the observed eye height of a driver; Object Height is a possible object in the path of a vehicle; and

Sight Distance is dependent on design speed and vehicle type.It is a major road safety design control when determining thehorizontal and vertical geometric alignment for a new orrehabilitation design.




16.3.3 Driver Eye Height / Object Height

Drivers eye height standards vary from 1.05m to 1.08m in differentcountries. The value has certain practical limits due to passenger carheights and the relatively small increases in the lengths of verticalcurves that would result. The values for use in the Philippines are inTable 16.2.

Table 16.2 : Driver Eye and Object Heights

Sight Distance Type Driver Eye Height (m) Object Height (m)

Car Stopping SightDistance 1.08 0.60

Truck Stopping SightDistance 2.33 0.60

Maneuver Sight Distance 1.08 0.60

Passing Sight Distance 1.08 1.08

Car Head-light to RoadSurface Sight Distance 0.60 ZERO

Truck to Car Tail-light SightDistance 2.33 0.60

16.3.4 Stopping Sight Distance (SSD)

There are two components in stopping sight distance:

Reaction Distance – the distance traveled while the driver perceives ahazard, decides to take action, then acts by starting to apply the brakesto start slowing down; and

Braking Distance – the distance required for the vehicle to slow downand stop.

Basic stopping sight distance assumes a straight alignment, a flatgrade, a wet surface with a reasonable amount of surface polishing,and an average amount of tire wear. Corrections need to be made forgrade and road curvature.

Reaction Distance

Reaction Distance depends on reaction time from the instant thehazard comes into view, to the instant that the driver actually appliesthe brakes. Reaction times vary, depending on driver ability andalertness. International studies of reaction time have been conducted.The studies show that for younger drivers, the reaction is less than forolder drivers. This is due to the ageing process that slows the reactiontime as people mature in age. It is for this reason that from a safetypoint of view, the standard adopts the reaction time for older people.

The reaction time to be used for road safety design is 2.5 seconds.This value is applied to the whole range of design speeds.




Reaction Distance = 0.278tV

Where:

t = Reaction time in seconds (2.5 seconds)

V = Design Speed (kph)

Braking Distance

The braking distance of a vehicle on a level roadway traveling at thedesign speed of the roadway = 0.039 V 2 /a, and on grade = V 2 /254[(a/9.81)±G].

Where:

f = Longitudinal friction factor between tire and roadway (seeTable 3.1 Highway Design Guidelines)

G = Percent of Grade divided by 100, (Uphill grades (+) andDownhill grades (-).

Stopping Sight Distance

If reaction distance is d1 and breaking distance is d2 then,

SSD = d 1 + d 2,

Where SSD = Stopping sight distance in meters.

SSD = 0.278tV + 0.039 V 2 /a, On level roadway

SSD = 0.278tV + V 2 / 254[(a/9.81)±G], Roadway on grade.

Sight distance and several stopping sight distance types are depicted inFigure 16.1. It can be observed that stopping sight distance for carsand trucks are the same distance when applied to different situations.Stopping Sight Distances for various speeds are in Table 16.3.

Table 16.3 : Stopping Sight Distance (SSD)

Design Speed (kph) Stopping Sight Distance (m)

20 2030 3540 50

50 6560 8570 10580 13090 160

100 185110 220120 250

Source : AASHTO – A Policy on Geometric Design of Highways and Streets, 2001




Figure 16.1 : Sight Distance Types




PC

Fi ure 16.3 : S iral and Circular Curve

PI

PI – POINT OF INTERSECTION




16.5 Vertical Geometry

16.5.1 Grades

Vertical alignment is the longitudinal profile along the centerline of theroad. It is made up of a series of grades and vertical curves. Theprofile is determined by a consideration of the planning, access,topographic, geological, design controls, earthworks and othereconomic aspects.

The maximum grades to be used on the national highways of thePhilippines are detailed in Table 16.1.

Flat Topography:

In flat topography , there are considerable lengths of national highway oftwo lane two way roads. The volume of traffic using these roads variesfrom location to location. However , there are sections of highway thatcould benefit from improved overtaking opportunity. The use ofovertaking lane geometry would give DPWH Region and Districtengineers and planners the facility to improve safety and the capacityof lengths of highway along which traffic has had a lack of overtakingopportunities. Details and traffic volume guidelines for providingovertaking lanes are detailed in Section 17.7, including the details oftapers at the diverge and merge locations.

A strategy for the implementation of a series of overtaking lanes alonglengths of national highway would provide cost efficient road works toimprove safety and overtaking opportunities that are currently lackingon lengths of national highway.

Rolling Topography:

Rolling topography may present additional need for auxiliary lanes fortwo reasons:

For the addition of overtaking lanes on flat to rolling grades; and

The provision for climbing lanes on steeper extended grades alongwhich trucks slow down to an extent where vehicles may beimpeded from passing due to lack of available overtaking sightdistance on the steeper grades. On steeper grades, AASHTOproposes limiting the maximum length to that which will not exceedthe critical length of grade generally as follows: The critical length isthat which will cause a typical loaded truck (5.5 kW/tonne) tooperate without an unreasonable reduction in speed. A reduction of15 kph is recommended, due to the significant increase in accidentinvolvement rate at high speed reductions.

The warrant for the design of climbing lanes is when truck speedsfall to 40 kph or less and traffic volumes equal or exceed those inTable 17.1.




In addition, climbing lanes should be considered where:

Extended grades over 8 % occur; Accidents attributable to the effects of slow moving trucks

are significant; Heavy trucks from an adjacent industry enter the traffic

stream on the upgrade; or The level of service E or F exist on the grade ‘E.’ Upgrade traffic flow rate in excess of 200 vehicles per hour Upgrade truck flow rate in excess of 20 vehicles per hour A 15 km/hr or greater speed reduction is expected for a

typical heavy truck. A reduction of two or more levels of service is experienced

when moving from the approach segment to the grade

The determination of the reduction of truck speeds on up grades(deceleration) and of the increase in speed (acceleration) areshown on Figure 16.5. These charts provide guidance relating to

the start and end locations of the climbing lane.

Mountainous Topography:

Although the speed of cars may be reduced slightly on steep upgrades,large differences in speeds of light and heavy vehicles will occur andspeeds of trucks will be quite slow. It is important, therefore, to provideadequate sight distance to enable faster vehicle drivers to recognizewhen they are catching up to a slower vehicle and to adjust their speedaccordingly. On steep down grades, it is desirable to increase theoperating speed of the individual geometric elements progressivelytowards the foot of the steep grade.

The topography in mountainous grades may not provide sufficient areafor climbing lanes to be provided. In these instances turnouts may beused. A turnout is a short section of paved shoulder or added lane thatis provided to allow slow vehicles to pull aside and be overtaken. Theydiffer from climbing lanes in their short length and different signing.Turnouts will be satisfactory to use on upgrades if traffic volumes arelow or construction costs very high.

In all the cases for the consideration of auxiliary lane provision , it isnecessary for the designer to consider a strategy for the placement ofthese facilities rather than consider them in isolation. The strategyshould look at a staging of the construction over lengths of highway toprovide the most economical benefits and maximize the road safety

gains.




Figure 16.5: Truck Speeds on Grades




16.5.2 Vertical Curves

The vertical alignment of a road consists of a series of straight grades joined by vertical curves. A vertical curve is expressed as a K value,which is the length of vertical curve in meters for 1% change in grade.In the final design , the vertical alignment should fit into the naturalterrain considering earthworks balances, appearance and themaximum and minimum vertical curvature allowed.

Large K value curves should be used where they are reasonablyeconomical.

Minimum K value vertical curves should be selected on the basis ofthree controlling factors:

• Sight distance is a requirement in all situations for driver safety;

• Appearance is generally required in low fill and flat topographysituations; and

• Riding comfort is a general requirement with specific need onapproaches to a floodway where the length of depression needsto be minimized.

Figure 16.6 provides details for the vertical curve theory and formulae.The adopted driver eye height and object height for cars and trucks aredetailed in Table 16.2. In summary, most vertical curves can bedesigned using the following equations:

Lv = KA

K = S 2 when S < Lv, and100 ( √h1 + √h2 )2

K = 2S _ 200 ( √h1 + √h2 )2 when S > LvA

where:

Lv = length of vertical curve (m)

K = length of vertical curve in meters for 1% change in grade

A = algebraic difference in grade (%)

S = sight distance (m)

h1 = driver eye height (m), refer Table 16. 2 (for cars and trucks)

h2 = object height (m), refer Table 16.2 (for cars and trucks)

For design purposes , the K value may be used to determine theequivalent radius of a vertical curve using R (radius m) = 100K.

Values for stopping sight distance are shown in Table 16.3.




Figure 16.6 : Symmetrical Vertical Curve




CREST CURVES:

Minimum crest vertical curve lengths for different values of A to providethe minimum stopping sight distance are shown in Figure 16.7. In thisfigure , the solid lines give minimum vertical curve lengths, on the basisof rounded values of K (length of eye=1.08m; height of object =0.60m)as determined from the following equations:

Lv = A S 2 when S is less than Lv658

Lv = 2S _ 685 when S is greater than LvA

On Figure 16.6, the short dashed curve crossing the solid linesindicates where S = Lv.

The vertical solid lines are the minimum lengths calculated as 0.6V (m).

Figure 16.7 : Crest Vertical Curves

Length of crest vertical curve (m)

A l g e

b r a

i c d i f f e r e n c e

i n g r a

d e

( % )




SAG CURVES

At least four different criteria are used for the establishment of sagvertical curves. These are: headlight sight distance, passenger comfort,drainage control and general appearance.

DPWH sag vertical curves are designed using headlight sight distancecriteria. Headlight height is 0.6 m as shown in Table 16.2. A 1 degreeupward divergence of the light beam is used in computing the length ofsag vertical curves.

The lengths of sag vertical curves are shown in Figure 16.8. Foroverall safety, a sag vertical curve should be long enough that the lightbeam distance is nearly the same as the stopping sight distance.

The K values of crest and sag vertical curves for the correspondingdesign speed and stopping sight distance are shown in Table 16.4.The K values for passing sight distance are also shown. The headlightsight distance for sags is equal to stopping sight distance.

The following directions shows the relationship between S,L at A usingS as the distance between the vehicle and point where the 1-degreeupward single of the light beam intersects the surface of the roadway;

When S is less than L When S is greater than L

As 2 120+3.5 S

120 + 3.5 S A

Where: L= length if sag vertical curve,

S= light beam distance,

A= algebraic difference in grades, percent

L = L = 25 -




17 CROSS SECTION

17.1 Introduction

The provision of adequate space for all road users includes vehicles,cyclists, pedicabs and pedestrians as well as other features such asshoulders, drainage, sidewalks, cut or fill slopes and clearances to theedge of the right of way.

The general cross section standards are detailed in Table 16.1, DesignStandards for Philippine National Highways.

17.2 Traffic Lanes

As indicated in Table 16.1, the basic lane width appropriate for nationalroads is 3.35 m.

On lower trafficked roads , the lane width can be reduced. This is justified on the basis of economics. For a single lane road traffic thelane width is 4.0 m. For a two lane national road the minimum width is2 x 3.35 m lanes (total 6.7 m). As the traffic volume increases , so theneed for extra width is justified. This width can increase up to amaximum of 3.65 m.

Where warranted and where road space is available, an additional lanecan be provided to improve safety of slow or vulnerable road userssuch as cyclists or pedicabs. An example of this is in Figure 17.1where the pedestrians have a sidewalk and bicyclists and tricyclistshave a separate lane separated from motor traffic.

Figure 17.1 : Good Cross-Section providing lane for vulnerable roadusers.




17.3 Shoulders

The shoulder width is generally selected according to the traffic volumeand standards are detailed in Table 16.1. Shoulder widths on lowvolume roads may be increased if there are a significant number of

pedestrians or other needs requiring use of the shoulder to improvesafety.

On curved alignments, it is advisable to consider the paving of theoutside curve shoulder width. This will minimize the possibility of avehicle that strays off the traffic lane from loosing control due to poortraction on a graveled shoulder. The widening of traffic lanes on curvedalignments is also advisable. This is dealt with in the DPWH HighwayDesign Guidelines.

Shoulder paving is a valuable method of providing:

integrity of the pavement;

width to place edgeline pavement markings;additional safety to prevent vehicles skidding or driverslosing control in gravel; and

low maintenance costs compared with unpaved shoulders.

Shoulder paving provides width for traffic when passing or maneuveringfrom oncoming vehicles and sheds water away from the regulartrafficked width.

For roads with less than 1,000 ADT, a shoulder is provided butgenerally not paved. A general exception might be at locations ofsharper than normal curves when the outside shoulder of a curve may

be paved. Sharp vertical curvature may warrant pavement wideningand shoulder paving to provide sufficient width for maneuvering traffic.

The paving of the shoulder width needs to be considered during theplanning and design stages. Paving of the shoulder is desirable forroads carrying over 1,000 ADT. The paving can then accommodatethe character of the traffic fleet, the maneuverability for passing needs,emergency parking, and periodical maintenance of the road.

17.4 Curb and Gutter

The concrete curb and gutter types may be barrier or mountable and

either include a gutter for drainage , or curb only. The curb crosssections are detailed in Appendix 6 and are listed below:

Barrier Curb & Gutter

Barrier Curb

Mountable / Drop Curb & Gutter

Mountable / Drop Curb




The use of the barrier or mountable curb types needs to be consideredin relation to the performance of vehicles that leave the traveled way forsome reason.

The barrier curb types are suited for the edge of the traveled waywhere it is generally considered that drivers should not mount the curbor sidewalk. The barrier curb types are used for areas where operatingspeeds are generally less than 60 kph and where parking of vehicles isallowed.

The mountable / drop curb types provide less vaulting of the errantvehicle on impact with the curb, less likelihood of the driver losingcontrol and less damage to occupants of the vehicles compared tobarrier curbs. The drop curb / mountable type shall be used for all trafficislands, medians and the right side of the roadway where operatingspeeds are greater than 60 kph.

17.5 Drainage

Longitudinal drainage ditches are essential part of any road that is noton fill and must be incorporated into the road cross section. These aredesigned to accommodate the expected rainfall but can often behazardous to vehicles that run off the road. Adequate attention musttherefore be given to the safety considerations of drainage facilitieswhen designing and upgrading highways.

Drainage ditches collect and disperse the water from the roadpavement and the runoff from the uphill side of the carriageway.However, a deep drain very close to the travel path of traffic can bevery hazardous if traffic strays from the traffic lane and this may causea driver to lose control. Careful design and location of such channelscan reduce the potential hazard.

It is desirable that open ditches being included in new works areconcreted and be provided with fitted pre-cast cover. This extends theclear zone width and forms a sidewalk for pedestrians.

Consideration to the covering of existing open concrete drainageditches and channels needs to be carried out in a logistical manner tocover the drainage structures where the need is greatest, such as inurban areas and on the inner side of curves in mountainous terrain.

In rolling or mountainous terrain the cross section width may not alwaysallow the construction of safe ‘vehicle friendly’ drainage structures.Sharp V-type and acute U-type drains are essential in many of theselocations. The use of precast concrete cover (with slots to permit theentry of water) on these drains should be considered, especially on theinner side of curves.

In flat and rolling terrain, the preference is to avoid safety hazardscreated by V-type and U-type drainage ditches. In this terraindevelopment of drainage ditches that can cope with the expectedrainfall levels and yet do not create unsafe conditions for motorists is achallenge to engineers.




The most important criteria to consider are:

Actual reconnaissance survey during wet whether to identifythe natural run-out locations;

Slopes on the side nearest the road should not be steeperthan 3:1 and preferable flatter as this will minimize accident

severity. The slope farthest from the road may be as steep asthe ground will permit;

L-type channels (concrete barrier curb and gutter) should beused where expected run-off will not breach the top of curb. Alarger than normal concrete gutter 600 mm wide may be anoption. Additional pits and careful selection of drainage run-out location to match natural run-outs is essential. L-typechannels are also safer and provide a walking area forpedestrians;

The U-type drainage channel offers no opportunity for avehicle to recover and no facility or space for pedestrians.Rural roads become the main pedestrian routes betweenBarangays and the absence of pedestrian footways forcespedestrians to walk on the road; and

Safe drainage provisions need to be considered when thebasic cross section of the road is being determined.

17.6 Pedestrian Facilities on Rural Roads

Walking is a major mode of transport in the Philippines and pedestriansform a high proportion of accident victims.

Special consideration need to be given to pedestrians along routesduring the design phase or re-planning stage of highway design.Surveys of pedestrian movements need to be conducted to identify thelengths over which priority needs to be given to provide pedestrianfacilities.

On higher trafficked roads, the non-motorized movements should besegregated either by providing a sidewalk or cycle-way beyond thedrainage facility, or on a segregated part of the road shoulder. Theprovision of wider shoulders with flatter cross slope also gives space forpedestrians in identified locations.

Sidewalks need not be expensive. Grading a path along one side ofthe road levels the ground and removes most of the vegetation tocreate a cheap segregated pedestrian facility. A regular maintenanceprogram should be initiated to ensure that the surfaces of pedestrianfacilities are kept reasonably clean and level and that vegetation doesnot cause an obstruction to either passage, visibility or to forcepedestrians onto the traveled way.




Visibility at crossing points is particularly important and advancewarning signs should be used for traffic, particularly if good visibility isnot available. On very low volume roads, reduced geometric standardswill reduce vehicle speeds and may allow pedestrians to use the roadsafely without segregation. This can lead to vehicles cutting cornersacross road shoulders used by pedestrians and creating an unsafe

situation. These locations should be surveyed to locate off -roadfootways at these points.

Where vehicle speeds are relatively high in Barangays and pedestriansare at risk, pedestrian crossing facilities may be protected by speedlimiting devices, such as roundabouts at road junctions , slow down orreduce speed signs, among others. Through Vehicle on through traffictends to travel at a relatively higher speed than does vehicle on localtraffic , and for this reason such speed limiting devices are a logical andbeneficial to the community. Parked vehicles should be banned within20 meters of each pedestrian crossing facility. The associatednarrowing of traffic lanes on the approaches to along with adequateroad signs and pavement markings will provide safety for the

pedestrians.

At culvert and bridge crossings, it is preferable for the road shoulder tocontinue across the structure to provide continuity of a pedestrianfacility. However, if the highway is narrowed, special segregationshould be made for cyclists and pedestrians. A segregated pedestrianfacility should continue across a bridge where surveys indicate theneed. A pedestrian barrier can further segregate pedestrians, however,the barrier terminals should be designed not to pose potential hazardsfor approaching vehicles and their occupants.

A pedestrian bridge adjacent to the bridge used by vehicles can be anoption where insufficient width is available for pedestrians. This can becantilevered off the structure of the road bridge. A minimum width of1.5 meters should be provided, although it may need to be wider forhigher pedestrian and cycle volumes. The additional cost will berelatively small if incorporated during the initial design and construction.

If a continuous pedestrian facility cannot be provided on longer bridges,then refuges at regular intervals, would be of assistance to pedestriansso they can move off the roadway when a vehicle is passing. Where apedestrian/cycle facility rejoins the road, it must be well signed and at agood point of visibility to drivers using the through road.

The provision of adequate space for all road users enhances safety.Alternatively, if vulnerable road users share space with vehicular trafficor if inadequate lane widths are provided for trucks, this can createsafety hazards.

17.7 Overtaking Provision (Auxiliary Lanes)

The need to provide overtaking opportunities is a major safety issue ontwo lane two way roads especially in rural areas where speeds arehigh. The other need for overtaking is when speeds of vehicles arereduced due to rolling or mountainous terrain.




In all cases of overtaking need , it is the vehicle that is overtaking thatgains the benefit of safety, improved travel time and removal offrustration caused by slower moving traffic.

The availability of overtaking opportunity depends on sight distance andgaps in the opposing traffic stream. As opposing traffic increases,overtaking opportunities become restricted even if sight distance isadequate. Sight distance that appears adequate may also be unusableon occasions due to the size of the vehicle in front, particularly on righthand curves. It is under this delayed travel condition that drivers aretempted to take risks when considering overtaking. The provision ofovertaking lanes removes this frustration and provides a safer andmore efficient highway at relatively low cost. The pavement can belocally widened to provide an overtaking zone for one direction oftravel, at low cost.

The selection of the location for overtaking lanes requires site visits toobserve traffic behavior and to select appropriate sites within theexisting road structure and at minimum cost and maximum driverbenefits.

17.7.1 Overtaking Lanes:

Overtaking lanes in flat to rolling terrain are used to break up platoonsof traffic and to improve traffic flow over a section of road. Theyprovide positive overtaking opportunities and are sometimes the onlyreal chance for overtaking to occur.

A series of such auxiliary lanes for both directions of traffic can greatlyimprove traffic flow and driver satisfaction. The desirable layout isbased on the start or end of the lane merging location being separatedby a 3 second distance of travel time. This distance is to minimize the

possibility of conflict between opposing merging vehicles. Anacceptable layout when the geometric considerations do not provide foran alternative is to allow the start of the merges to be opposite oneanother.

The provision of overtaking lanes may delay the need for a majorupgrading to provide dual carriageways. Where a four lane road hasalready been provided and the traffic volumes are consistently high, theneed for auxiliary lanes on grades may still arise when there is a highproportion of heavy vehicles.

The traffic volume guidelines for the provision of overtaking lanes areshown in Table 17.1.




Table 17.1 : Traffic Volume Guidelines for Provision of Overtaking Lanes

Overtaking Opportunitiesover the Preceding 5 km (1) Design Volume (ADT)

Description of the

Ability to Overtake

PercentageLength

ProvidingOvertaking (2)

Percentage of Slow Vehicles (3)

5% 10% 20%Excellent 70-100 6,000 5,000 4,000Good 30-70 5,000 4,000 3,500Moderate 10-30 3,000 3,000 2,500Occasional 5-10 2,500 2,000 1,500Restricted 0-5 1,500 1,500 1,000Very Restricted (4) 0 1,000 1,000 500

Notes:

(1) Depending on road length being evaluated, this distance could

range from 3 to 10 km.

(2) See following text.

(3) Include light trucks and cars towing trailers and other units.

(4) No overtaking for 3 km in each direction.

The proportion of road length offering overtaking provision is the sum ofsuch section lengths, divided by the total road length being considered.

OP = ∑ OLs x 100TSL

Where:OP = Proportion of road offering overtaking provision (%)

∑OLs = Sum of overtaking lengths in road section (m)

TSL = Total road Length (m).

The recommended lengths of overtaking lanes relative to the operatingspeed of the road section are shown in Table 17.2.




Table 17.2 : Overtaking Lane Lengths

OperatingSpeed(kph)

Overtaking Lane Lengths - excluding Taperlengths (m)

Minimum DesirableMinimum

NormalMinimum

50 75 225 32560 100 250 40070 125 325 47580 200 400 65090 275 475 775

100 350 550 950110 420 620 1070

Note: The start and terminal areas of overtaking lanes should belocated where they are clearly visible to approaching drivers.

17.7.2 Climbing Lanes

Climbing lanes can be considered as a special form of overtaking lanebut they are only provided on inclines. Climbing lanes form part of thenetwork of overtaking opportunities and will therefore have an effect ondecisions associated with the location of other overtaking lanes.

The warrant for climbing lanes is where:

• Truck speeds fall to 40 kph or less;

• Truck speeds reduction by more than 15 kph;

• Upgrade traffic flow rate in excess of 20 vehicles per hour;

• Upgrade truck flow rate in excess of 20 vehicles per hour;

• Extended grades over 8% occur;

• Level of service E or F exist on the goods;

• Accidents attributable to the effects of slow moving trucks aresignificant;

• A reduction of two or more levels of service is experience whenmoving from the approach segment to the grade; and

• Heavy trucks from an adjacent industry enter the traffic stream.

Table 17.2 indicates the lengths on constant individual grades neededto produce a reduction in truck speed to 40 kph.

Truck speeds on grades can be assessed using the curves included inFigure 16.5 and the longitudinal section of the road. The decelerationchart in Figure 16.5 assumes a truck entrance speed of 100 kph.




17.7.3 Merging and Diverging for Auxiliary Lanes

The design of overtaking lanes and climbing lanes requires theconsideration of the:

Initial diverge taper;

Auxiliary lane length; and

End or merge taper.

Diverge Taper

A taper is required at the start of an auxiliary lane to provide for thelateral movement of traffic.

A diverge is the dividing of a single stream of traffic into separatestreams as shown in Figure 17.2. The diverge taper length for athrough traffic lane is based on a lateral shift movement of traffic of 1m/s. A lateral shift of 1 m/s means that for every second of travel in thelongitudinal direction, there is a transverse movement of 1 meter.

Diverge Taper – 1.0 m/s lateralshift for a through lane

Figure 17.2 : Diverge Taper

The taper lengths for various speeds and lane widths are in Table 17.3.

Merge Taper

A merge is a converging of separate streams into a single stream asshown in Figure 17.3.

A merge taper length is based on a lateral shift movement of traffic of0.6 m/s for a through lane merge and 1.0 m/s for an acceleration lanetaper. A lateral shift of 0.6 m/s means that for every second of travel inthe longitudinal direction, there is a transverse movement of 0.6 meter.




Merge Taper:- 0.6 m/s for through lane merge- 1.0 m/s for acceleration lane merge

Figure 17.3 : Merge Taper

The lengths provided for the diverge and merge movements areimportant to enable adequate notice and opportunity to complete themovement safely.

Table 17.3 : Diverge and Merge Lengths

Design Speed 3.7 3.6 3.5 3.4 3.3 3.2 3.1 3.0

3. 6

50 (13.88 m /s) 51 50 49 47 46 44 42 4260 (16.67 m /s ) 62 60 58 57 55 53 52 5070 (19.44 m /s ) 72 70 68 66 64 62 60 5880 (22.22 m /s ) 82 80 78 76 73 71 69 6790 (25.00 m /s ) 93 90 88 85 83 80 78 75

100 (27.78 m /s ) 103 100 97 94 92 89 86 83110 (30.56 m /s ) 113 110 107 104 101 98 95 92120 (33.33 m /s ) 123 120 117 113 110 107 103 100

50 (13.88 m/s) 86 83 81 79 76 74 72 6960 (16.67 m /s) 103 100 97 94 92 89 86 8370 (19.44 m/s) 120 117 113 110 107 104 100 9780 (22.22 m /s ) 137 133 130 126 122 119 115 11190 (25.00 m /s ) 154 150 146 142 138 133 129 125

100 (27.78 m /s ) 171 167 162 157 153 148 144 139110 (30.56 m /s ) 188 183 178 173 168 163 158 153120 (33.33 m /s ) 206 200 194 189 183 178 172 167

Lane Widths

Taper Lengths @ 1.0 m/s lateral shift [(Des ign Spee d/3.6 x Lane Width) Shift]

Taper length @ 0.6 m/s lateral shift

Design Speed(kph)

17.7.3 Slow Vehicle Turn-outs:

A turn-out is a very short section of fully constructed shoulder or addedlane that is provided to allow slow vehicles to pull aside and beovertaken. It differs from an overtaking lane due to its short length,different signing and that the majority of vehicles are not encouraged totravel in the right lane. A turnout may be appropriate if traffic volumesare low or construction costs are very high for an overtaking lane orclimbing lane.




Turn-out lengths of 60 to 170 m for average approach speeds of 30 to90 kph respectively and a width of 3.7 m are to be used. Care must betaken to provide adequate sight distance.

Signing at the start and merge points are required to better indicatediverge and merge locations. The minimum sight distance should bestopping sight distance for the section operating speed.

17.7.4 Descending Lanes:

On steep down grades the speed of trucks will be as low as that onequivalent up grades. There will be a similar effect on traffic flow ifovertaking opportunities are not available. A descending lane may beappropriate in these circumstances.

Sight distance provision at the terminals is also important. Whenpassing sight distance warrants, overtaking will be readilyaccomplished. Similarly, if a climbing lane is provided in the oppositedirection and the passing sight distance is adequate, overtaking slower

downhill vehicles can be safely achieved and a descending lane will notbe needed.

Where the down grade is along sharp horizontal curves , a descendinglane will be appropriate to provide satisfactory traffic operation. Designdetails are similar to those of climbing lanes.

17.7.5 Emergency Escape Ramps:

Where long steep grades occur , it is desirable to provide emergencyescape ramps. These are to be located to slow or stop an out ofcontrol vehicle away from the main traffic stream. Out of controlvehicles result from drivers losing control of their vehicle.

There are four types of escape ramps:

• Sand Pile;

• Descending Grade;

• Horizontal Grade; and

• Ascending Grade.




Each one of the ramp types is applicable to a particular situation wherean emergency escape ramp is desirable and must be compatible withthe location and topography. The most effective ramp is an ascendingramp with a full depth arrester bed. The length of ramp can beassessed from:

L = V2 / (26a + 2.55g 1)

Where:

L = length of arrester bed excluding 50 m transition at the start(m)V = Entry speed (kph)a = deceleration - (3.0 m/sec 2 for 350 mm deep gravel)

- (3.7 m/sec 2 for 450 mm deep gravel)g1 = grade (%) (positive for upgrade ; negative for downgrade).

The provision of escape ramps requires careful consideration of sitefactors including the land use adjacent to the exit. Existing roads andstreets used for property access should only be used where the trafficvolume is very low and there is very low probability of an escapingvehicle meeting another vehicle.




18 DELINEATION

The guidance of drivers as they travel along a length of road isimportant to provide safe travel conditions.

Delineation of the road alignment needs to be considered as part of thedesign process to ensure that adequate guidance is provided to roadusers. Improving delineation may also be needed to improve safety ona road section experiencing traffic accident problems.

Good delineation enables a driver to laterally position the vehicle on theroad and to be aware of the changes in direction or alignment that maybe ahead. Delineation is particularly important during periods of poorvisibility e.g. at night or during rain or fog.

Figure 18.1 : Good Road Delineation

Delineation is generally provided by the use of the following devices:

Pavement MarkingsCenter lineLane linesEdge lines or tactile edge linesOther painted markings e.g. islands, hatchingReflective Pavement Studs (RPS)

SignsWarning signs indicating curves etc.

Hazard markersChevron signs for substandard curves

Guide posts

Reflective delineators

Lighting

Curb or other physical devices




Examples of poor road delineation are shown in Figures 18.2 and 18.3.

Figure 18.2 : Poor Curve Delineation

Figure 18.3 : Poor Delineation of the Center and Edge of Roadway

Figure 18.4 : Examples of Chevron Signs providing Delineation of Curves




Figure 18.5 : Road Delineation affected by shadows

In Figure 18.5 , shadows across the roadway affect delineation of theroad alignment. Adding edge lines or chevron signs could improve thedelineation.

Details regarding the selection and use of signs and pavementmarkings for delineation are provided in DPWH Highway Safety DesignStandards Manual Part 2: Road Signs and Pavement MarkingsManual.




19 INTERSECTIONS

This section of the manual describes the safety features ofintersections and the criteria for safe design.

An intersection is the junction where two roads either cross or meet.

19.1 Intersection Types

The types of intersections that generally exist on the road network are:

Unflared and unchannelized intersections (without widening ortraffic islands);

Flared and unchannelized intersections (with widening butwithout traffic islands); and,

Channelized intersections (traffic islands to guide traffic).

The types of intersections are also described in Section 4.1.3 of theDPWH Highway Design Guidelines.

Common types of intersection are cross intersections, T-intersections,Y-intersections, other multi-legged junctions and roundabouts.

Principles of good design to reduce the likelihood of traffic accidentsinclude:

Minimize the speed of vehicles at potential collision points;

Separate movements and points of conflict by channelization, orin some situations, prohibit certain movements (and provide forthem at other intersections along the route);

Control movements to reduce the possibility of conflict; and

Clearly define vehicle paths by use of pavement markings.

19.2 Traffic Control Devices

Traffic can be controlled at intersections by regulatory signs, trafficsignals, roundabouts. If no traffic control devices are provided, itoperates according to the road rules in Chapter IV – Traffic Rules, inRepublic Act No. 4136 ‘Land Transportation and Traffic Code’.Whatever type of traffic control is used, it must be clear and visible to

drivers from a distance that will allow the motorist to react and stop ifnecessary.

All intersections should have appropriate pavement marking, not only toensure vehicles stop at the correct position, but to also help define theintersection area.

Where intersections have no traffic control device other than pavementmarking, vehicles are required to give way to other vehicles that are




already in the intersection or have reached the intersection first and areabout to enter.

19.2.1 Priority Intersections

Stop or Give Way signs facing the minor road approaches at anintersection are used to give priority to the major road. Safety at anintersection is improved by assigning clear priority to inform drivers oftheir responsibilities.

A Stop sign is installed on the minor road if the visibility to traffic on themajor intersecting road is below specified distances relative to themajor road operating speed. Otherwise a Give Way sign is used.

The Highway Safety Design Standards Part 2: Road Signs andPavement Markings Manual, Sections 2.6.1 and 2.6.2 provide detailson the visibility requirements for the use of Stop and Give Way signs.

19.2.2 Signal Controlled Intersections

Traffic signals improve safety and simplify decision making. They also:

Separate vehicle movements in time. This minimizes conflicts.

Minimize delays at an intersection;

Enable vehicles from a side road to cross or enter the majorroad; and

Assist pedestrians in crossing the road.

19.3 Control of Conflicts

A conflict point occurs where two travel paths interact or cross. Safeintersection design uses the following principles:

Minimizing the number of conflict points;

Minimizing the area of conflict;

Separating points of conflict;

Giving preference to major movements; and

Minimizing relative speed of conflicting movements.

A large area of conflict can occur when roads intersect at an acuteangle, where wide roads intersect or with offset cross intersections.




Figure 19.1 shows anintersection with a largearea of conflict. Thiscould be a saferintersection withchannelization of the

movements or bycontrolling movementswith a roundabout ortraffic signals.

Figure 19.1 : Large Intersection Conflict Area

The number of conflict points depends on the type of intersection.Figures 19.2 to 19.4 demonstrate where the conflict points occur forvarious types of intersection. Table 4-1.2 of the DPWH HighwayDesign Guidelines also refers to intersection conflict points. Thefigures below show the major points of conflict for crossing and mergingmovements. The diverging conflicts are not shown as they aregenerally of a minor nature and would usually occur prior to theintersection, rather than within the intersection itself. Generally, from asafety point of view, the fewer conflict points the safer the intersection.

6 points of major conflict

Figure 19.2 : Three-Legged Intersection

24 points of major conflict

Figure 19.3 : Four-Legged Intersection




4 points of major conflict Figure 19.4 : Roundabout at Four-Legged Intersection

19.4 Control of Speed

The speed of vehicles through an intersection depends on: Alignment;

Road environment;

Traffic volume and composition; and

Traffic control devices.

19.4.1 Relative Speed

The safety of an intersection depends largely on achieving low relativespeeds. Relative speed is the vectorial speed of convergence of thevehicles in a conflict maneuver. In each of the figures below, it can be

seen that the higher the collision angle the higher the relative speed.

Figure 19.5 : Cross Road

A = 60 kph

B = 60 kph

Relative SpeedC = 85 kph




Figure 19.6 : Y Intersection Layout

Figure 19.7 : Roundabout

19.4.2 Attaining low relative speeds

Low relative speed conditions at intersections can be obtained by:

Choosing a layout where conflicting movements cross at anglesless than or equal to 90 degrees;

Providing a layout or alignment that slows down approachingvehicles; and

Providing deceleration lanes.

A common intersection type where the layout can be hazardous is theY-junction or T-junction with two way traffic each side of a singletriangular island (refer to Figure 19.8 below). These layouts have six(6) points of conflict similar to other 3-legged intersections. However,they can be less safe due to the angles of conflict involved (at points A,B, and C), as there is a potential for high speed high severity head on

accidents. A driver’s view of approaching traffic on the intersectingroadway also creates a difficulty in seeing possible conflicts. Effectivetraffic control using signs to define priority for the major movement isalso difficult to achieve.

A = 60 kph

B = 60 kph


A = 20 kph

B = 20 kph





Figure 19.8 : Conflicts at Y and T Intersections

19.5 Channelization

Channelization at an intersection involves the control of traffic byprovision of traffic islands or pavement markings to direct the traffic intopredetermined paths. The shape of an intersection layout andchannelization depends on the layout of the approaching roadways, thetraffic patterns and control strategy, traffic volumes including turningmovements, pedestrian needs, parking arrangements and access toabutting properties. Channelization can be used to:

Merge traffic streams at small angles to ensure low relativespeed between conflicting stations

Reduce areas of conflict by causing opposing traffic streams tointersect generally at right angles (desirable range is in the orderof 70 to 90 degrees);

Improve and define the alignment of major movements;

Control the speed of traffic entering an intersection by changingalignment or bending their approach path;

Control the speed of traffic by restricting width or funneling;

Provide a refuge or median to shelter a turning or crossingvehicle;

Provide protection for pedestrians;

Improve conspicuity of an intersection e.g. a splitter island on anapproach;

Prohibit certain turns/movement; and

Provide locations for traffic signal poles or traffic signs.

In the design and layout of channelization care should be taken toprovide clear guidance to drivers with simple decision making and toavoid any possible cause of confusion.




19.6 Lane widths

The width of through traffic lanes at an intersection can affect howmotorists behave on the approach and within an intersection.

If lanes are too wide then it can encourage drivers to travel at high

speeds or form extra lanes of traffic. It can also result in poor lanedelineation.

Lane widths at intersections may be less than midblock lane widths toenable additional through or turning lanes to be provided for reasons ofsafety or capacity.

Narrow lanes need to be avoided where single lane roadways havecurbs on both sides e.g. on slip lanes, as there needs to be sufficientwidth for vehicles to get past a stalled vehicle. It is desirable to provideat least 5m between curbs to enable passing of a stalled vehicle.

Turning lanes within an intersection need to provide for the swept path

of turning vehicles. It is also desirable to provide at least 5m betweencurbs on slip lanes to cater for the swept paths of larger vehicles duringthe turn.

When designing an intersection, turning templates should be used toindicate the “swept path envelope” for various angles of turn. Anexample template is shown in Appendix 2. These are used to ensurethat there is enough pavement width on which the vehicle can turn andto ensure that the vehicle will not encroach into an adjacent lane oroverhang areas with poles or signs. These are placed on the layoutdesign to ‘map’ the areas of the wheel paths and the truck overhang.

A computer program called AUTOTURN can also be used to ‘map’ the

swept path of large vehicles.

19.7 Auxiliary Lanes at Intersections

Auxiliary through traffic lanes may be provided at urban signalizedintersections to increase capacity. An auxiliary lane may also berequired through a roundabout to provide appropriate capacity.

Tapers are required at the start and end of auxiliary lanes to provide forthe lateral movement and merging of traffic. Details of diverge andmerge taper lengths for auxiliary through lanes are detailed in Section17.7.3.

For right and left turn lanes the diverge tapers are shorter so that thecommencement of the lane is more obvious and so the driver isrequired to make a conscious decision to change lanes. Typicallengths are:

Urban area (up to 70 kph) - 30 m taper

Rural or high speed area up to 80 kph – 40 m taper

Rural or high speed area up to 100 kph – 50 m taper




19.8 Right and Left Turning Lanes

The safety of an intersection can be improved by provision of right andleft auxiliary turning lanes. Turning lanes also improve intersectioncapacity and traffic flow. They are particularly important if the volumeof traffic making these moves is high or if the through or oncoming

traffic flows are high.

Provision for turning lanes can generally be provided in the followingways:

• Shared turning and through lane;

• Flaring and taper; or

• Separate lane for deceleration and storage.

Figure 19.9 can provide guidance on choosing an appropriatetreatment in rural or outer urban locations.

Notes:QT – Traffic flow in peak hour of through traffic (vehicles / hour)QL – Traffic flow in peak hour of left turn traffic (vehicles / hour)QR – Traffic flow in peak hour of right turn traffic (vehicles / hour)If peak hour volumes are not available, assume the design peak hour volume equals10% to 15% of the ADT.

Figure 19.9 : Guideline for Left and Right Turn Lanes

At some intersections there may need to be two or more turning lanesto cater for high turning volumes. The provision of slip lanes for rightturning traffic is also desirable where space is available. The type oftreatment used depends on the volume and composition of the trafficwanting to make the move.




The auxiliary lanes used for turning traffic are provided to allow vehiclesto decelerate in a separate lane, avoiding delays for through trafficvehicles and to provide an area for vehicles while waiting to make theturn.

It is important from a safety point of view that the length of the auxiliarylane is adequate to store waiting vehicles and to ensure that vehiclesdo not queue out into the adjacent lane and create a hazard for throughtraffic.




19.9 Right Turn Slip Lanes

Right turn slip lanes are provided to minimize the delays for rightturning vehicles and to make the right turn movement easier and safer.

A traffic island is provided with this treatment to: Guide traffic into defined paths;

Separate through, turning and opposing traffic movements;

Give advance warning of the intersection to approaching drivers;

Provide refuge for pedestrians; and,

Prohibit undesirable or unnecessary traffic movements.

The provision of an auxiliary right turning lane in advance of the sliplane is desirable. The length is generally based on the distanceneeded for deceleration with consideration also given to the storagerequirements for turning traffic. An auxiliary lane also enables turningtraffic to enter the lane around the queued through vehicles.

The two types of slip lane arrangements are:

High entry angle slip lane; and

Free Flow Slip Lane.

The shape and size of the traffic island is important to guide vehiclesalong a path where a safe intersecting angle or merging can beprovided with traffic in the intersecting roadway. The choice of layoutarrangements depends on site conditions.




19.8.1 High Entry Angle Slip Lane

4.0

4.4 min

1

Figure 19.10 : High Entry Angle Slip Lane

The treatment in Figure 19.10 allows vehicles to wait at the hold line atan angle of about 70 degrees, which ensures good visibility ofapproaching traffic in the intersecting road. A lower angle promotes ahigher speed movement and can also create difficulties for the driverseeing vehicles approaching from the left.




19.8.2 Free Flow Slip Lane

30m

Notes:

* - Offset of 0.2 m per 10 kph of approach speed

W – Width based on swept path of turning vehicleincluding space to overtake a broken down vehicle (ifcurbs on both sides)

R1 – Turn radius design speed based on 50% to 80%of through speed

Offset 0.3m

0.3m0.6R

in 10 Taper

Acceleration (speed change) LaneRefer AASHTO Exhibit 10.73Includes merge taper 1.0 m/slateral shift

R1

Figure 19.11 : Free Flow Slip Lane

The type of treatment in Figure 19.11 is appropriate when there is ahigh volume of right turning traffic and a low pedestrian volume (thefree flow slip lane does not cater as well for pedestrians due to thehigher speeds). The free flow slip lane arrangement may be suitable ina rural situation or an expressway interchange.

19.10 Left Turn Treatments

Provision of a special treatment for left turning vehicles at intersectionsis dependant on the total number of vehicles needing to make themovement and the opportunities available for the move to becompleted.

Three types of treatments that could be used, depending on the trafficvolumes and road environment are shown in Figures 19.12, 19.13 and19.14.




Figure 19.12 : Type A Left Turn Treatment

The Type A treatment in Figure 19.12 has no separate turning lane andis appropriate when the left turn volume is low. A feature of thistreatment is sufficient width to allow passing of left turning vehicles.This area of shoulder could be paved in the vicinity of the intersectionas a measure to improve safety and reduce maintenance.

Figure 19.13 : Type B Left Turn Treatment

The Type B layout in Figure 19.13 has a semi-protected left turn lane.It is safer than a Type A treatment, as it provides a full width markedlane for through vehicles to pass waiting left turners. This treatment isused for higher left turn volume situations.

The length D 1 in the treatment above is based on a diverge movementwith a lateral shift of 1.0 m/s. Appropriate lengths for various operatingspeeds are shown in Table 19.1. The length D 2 needs to allow forstorage of waiting vehicles and would generally be in the range of 20 to50 meters. The radius R is based on the design speed.

Figure 19.14 : Type C Left Turn Treatment




The Type C layout in Figure 19.14 shows a protected left turntreatment. It features a formalized auxiliary turning lane with a paintedisland to shelter a vehicle waiting to turn left. This treatment isappropriate for high speed roads with significant left turn volumes.

The length D 1 in Figure 19.14 is based on a diverge movement with alateral shift of 1.0 m/s. Appropriate lengths for various operatingspeeds are shown in Table 19.1. The length of the deceleration taperentering the left turn lane would reduce to 30m in an urban or lowspeed environment.

19.11 Intersection Capacity

The safety of at grade intersections is largely dependent on how wellthe traffic demand is catered for.

The capacity of an intersection depends largely on the number of lanesprovided and whether auxiliary lanes are provided. For a signalizedintersection the phasing and cycle times also have an impact on thecapacity of the intersection.

Intersections without traffic signals are appropriate low traffic volumes.For higher volumes auxiliary lanes and signals need to be considered.

When the flow on the major leg is high, it can become an issue forvehicles from the minor road as they can have trouble entering orcrossing the major road. This is a safety concern as they can decide tochoose smaller gaps which increases the risk. Vehicles wanting to turnoff the major road can delay through vehicles on the major road, ifauxiliary lanes are not provided.

19.12 Sight Distance at Intersections

Safe intersection design requires that the appropriate sight distance beprovided. The Stopping Sight Distance (SSD) values used for roadsections are also applicable to the major road at intersections.

SSD values for various design speeds are based on the stoppingdistance plus the travel distance during the reaction time. These areoutlined in Table 16.2.

Where possible , Intersection Sight Distance (ISD) should also beprovided. The ISD applicable to drivers in the minor road enablesvehicles from the minor road to enter or cross the major road withoutimpeding the traffic on the major road. ISD values for various designspeeds are outlined in Table 19.1.




Table 19.1 : Intersection Sight Distance (ISD)

Design Speed (kph) Stopping SightDistance (m)

Intersection SightDistance (m)

20 20 45

30 35 65

40 50 85

50 65 105

60 85 130

70 105 150

80 130 170

90 160 190

100 185 210

110 220 230

120 250 255

19.13 Horizontal and Vertical Intersection Geometry

Sight distance standards should be provided for both horizontal andvertical alignments.

The optimal location of intersections is on straight alignments with

uniform grade. This situation provides the best situation for sightdistance requirements and also the driving task is simplified as vehiclescan be maintained more easily on correct paths through theintersection. For the same reason, severe changes of alignment withinan intersection should be avoided.

Where a straight alignment cannot be achieved, the position ofintersections should be contained within a horizontal curve , so thatdrivers are already traveling on the curve before reaching theintersection.

In rolling terrain, intersections should be positioned on sag curvesrather than near crest curves, as sight distances can be restricted.

Sight distance restrictions can also occur when the minor roadintersects on the outside of a horizontal curve. In this situation , thesuperelevation on the major road is sloping away from the minor roadand the pavement may not be visible to the minor road driver,particularly if the minor road is on an upgrade approaching theintersection. To improve conspicuity of the intersection in this situation,it may be possible to regrade the minor road approach to theintersection or provide a splitter island.




19.14 Roundabouts

19.14.1 Introduction

A roundabout (or rotunda) is one of the safest type of intersectiontreatments. It consists of a circular island in the middle of anintersection and traffic moves around it in an anticlockwise direction.

When designed correctly , the roundabout is probably the safest type ofintersection as there are fewer conflict points. In addition, traffic isslowed down by the layout before entering the roundabout, the relativespeed at possible collision points is low and the decision making fordrivers is simple. The provision of splitter islands on the approach to aroundabout also provides advance notice to the driver and controlsvehicle movements.

19.14.2 Safety Benefits

Roundabouts are a safe and effective form of intersection control as thecentral island physically deflects the traffic through the intersection andcontrols the speed of traffic. Any collisions that may occur in aroundabout are generally less severe because traffic is moving slowlyand in the same general direction. In addition, drivers only look fortraffic on the left, making it easier to judge an entry into the intersection.

19.14.3 Appropriate Locations for Roundabouts

Many factors need to be taken into consideration when choosing thetype of intersection to be provided at a given location. Roundaboutsmay be appropriate in the following situations:

At intersections with high accident rates

When physical control of speed is desirable

When the flows on each approach are balanced and capacityanalysis indicates that volumes can be managed;

When the volume of left turners is significant

If traffic signals may be inefficient e.g. due to a large number ofphases; and

For multi-legged intersections.

Roundabouts may not be appropriate in the following situations:

Where satisfactory geometric design cannot be provided due toinsufficient space of unfavorable topography;

Where unbalanced flows with high volumes are on one or moreapproaches;

Where a major road intersects a minor road and a roundaboutwould result in unacceptable delay to the major road; or

Where there is considerable pedestrian activity and due to hightraffic volumes it would be difficult for pedestrians to cross at theintersection.




19.14.4 Balanced Flows

Roundabouts operate best when the traffic flows are balanced. Thisdoes not necessarily mean that all movements must be of the samemagnitude but that the predominant movements are “broken up” bycirculating traffic so that gaps are provided to allow vehicles waiting onadjacent legs to enter the roundabout without major delays.

When traffic flows are not balanced then significant delays can beexperienced by traffic on the minor roads.

19.14.5 Roundabout Design Practice

The main components of a roundabout are shown in Figure 19.15

Figure 19.15 : Geometric Elements of a Roundabout

The following points outline good practice in the use and design ofroundabouts:

Roundabouts can be used to improve safety at any type ofintersection, including urban or low speed environments as wellas rural or high speed environments. The principles of gooddesign provide for control of vehicle speeds by using an




appropriately designed central island as well as approach anddeparture geometry to control vehicle speeds.

The central island should preferably be circular to keep thedriving task simple. However, in some locations if there areconstraints or layout issues limiting an appropriate design speeddue to approach widths or angle of approach, other shapes e.g.egg shape, can be considered. Guidelines on the size of thecentral island are in Section 19.14.7 Step 4. The size of thecentral island is generally related to:

Widths and location of approach roads;

Design speed and deflection necessary; and

Available space.

At urban low speed roundabouts , the deflection is provided bythe circular island in the intersection. Splitter islands on theapproach assist in providing deflection and restrict ‘wrong way’movements.

Figure 19.16 : Inner Urban Roundabout.

The layout in Figure 19.16 could be improved with splitterislands to guide drivers and control the entry of traffic into theroundabout.




Figure 19.17 : Outer Urban Roundabout

At rural roundabouts where the approaches are high speed,deflection has to be provided earlier by longer splitter islands onthe approach before vehicles reach the intersection.

Figure 19.18 : Rural Roundabout

It is important that the approaches are designed to graduallyslow traffic down before reaching the circulating roadway. Themaximum design speed through the roundabout should

generally be 40 kph in urban areas and no greater than 50 kph inrural areas.

Once a vehicle has entered the circulating roadway, it should beable to exit quickly. The departures should be designed with atangential straight or high radius curve departure.




Figure 19.19 – Urban Splitter Island Details : Low Speed Approach

Figure 19.20 : Urban Splitter Island

On high speed roads, the splitter island should generally extendacross the full width of the approach lanes as seen by theapproaching driver. The length should provide for adequatedeflection and deceleration.




Figure 19.23 : Number of Lanes

3. Establish the space available for the roundabout taking intoconsideration site controls such as property boundaries, utilities, trees,parking etc.

4. Select a trial central island diameter and determine the width neededfor the circulating carriageway. Refer to Figure 19.24 and Table 19.2.As a guide, the diameter of the central island should be 5 to 20 mdiameter in an urban environment and 20 to 50m in a ruralenvironment. Larger radius islands are used on divided carriagewayroads or high speed roads. If large vehicles are going to be using theintersection then a desirable minimum central island radius of 8.0m ispreferred. This then enables the use of a 15m radius (outside radius ofturn path) turning template.

Figure 19.24 : Turning Radius for Determining Circulating CarriagewayWidth




Table 19.2 : Circulating Carriageway Widths

5. Position the central island on the plan and sketch splitter islands andentry/exit lanes, ensuring that the offsets to the splitter islands aremaintained.

6. Check if adequate deflection has been achieved for the desired designspeed. If not, adjust the layout including the entry and exit geometryand the position or size of the central island. Refer to Figure 19.25 or19.26 (multilane roundabout).

Radii curves for various design speeds are attached as Appendix 4. Thesecan be copied as transparencies and used to check the deflection criteria.




Figure 19.25 : Deflection Requirement – Single lane

Figure 19.26 : Deflection Criteria – Multi Lane

7. Check sight distances on each approach in relation to horizontal andvertical visibility.

The alignment on the approach should be such that the driver has agood view of the splitter island, the ‘Give Way’ line, the central islandand desirably the circulating carriageway.

At roundabouts, the speed of vehicles is controlled within the circulatingcarriageway, however, it is also desirable that drivers approaching theroundabout are able to see other entering vehicles before they reachthe ‘Give Way’ line, particularly in a rural or high speed area.Therefore , a stopping sight distance requirement based on a 50 kphapproach speed is also desirable. In urban areas , this criteria can bedifficult to achieve.

A driver stationary at the ‘Give Way’ line should have a clear line ofsight to the left to approaching traffic in the circulating carriageway andvisibility to traffic entering the roundabout from the approachimmediately to the left, for a distance representing the travel time equalto the critical acceptance gap. A critical gap of 4 to 5 seconds isappropriate.

8. Check turning path requirements using the appropriate turning pathtemplates or a software package such as ‘Autoturn’. There are varioussoftware packages available and they are valuable computer designtools.

9. Finalize the edge of pavement design at each entry and exit includingthe splitter island details, providing the appropriate nose radii andoffsets.




10. Ensure that other road users such as pedestrians and cyclists arecatered for in a safe manner.

11. Design the lane and pavement markings. Refer to Road Signs andPavement Markings Manual for details of roundabout pavementmarkings.

Figure 19.27 : Typical Pavement Markings at a Multi Lane Roundabout

12. Complete a signing design. Refer to Road Signs and PavementMarkings Manual for details of roundabout signs

13. Complete a lighting design.

14. Complete a landscaping design ensuring that sight distancerequirements will be maintained when plants are fully grown.

19.14.8 Traffic Control and Priority

Priority at roundabouts is given to circulating traffic within the roundaboutby installing Give Way signs facing all approaches.

Roundabouts operate efficiently when the entering traffic gives way andwaits for a gap in the circulating flow before entering the roundabout. Thisoperation enables circulating traffic to leave the roundabout without delay.It also reduces congestion and the likelihood of the roundabout ‘locking up’.




The Give Way signs should be placed on both sides ofan approach where it is two or more lanes wide.

Figure 19.28 : Give Way Sign (R1-2)

In congested situations where the traffic flow on oneapproach is very heavy and it prevents traffic on another approach fromentering the roundabout, it is possible to install traffic signals on theapproach with the heavy traffic to stop it during busy times and allowtraffic on the minor approach to enter. Where this type of control isused the signals are usually activated with loops to detect queuelengths.

19.15 Examples of Poor Intersection Layouts

19.15.1 Y-Intersection

Example of poorintersectionlayout – roadcan giveimpression thatit goes straightahead(especially atnight), poorcurvedelineation.

Figure 19.29 : Poor Intersection Layout

G I V EWA Y




Poor layout andno pavementmarking. Notclear thatvehicles on thisleg need to giveway.

Figure 19.30 : Poor delineation




19.15.2 Y-Intersection with Triangular Island

Poor IntersectionLayout – highrelative conflictspeeds, difficultydefining priority,awkward layoutto see vehicleson intersectingroadway, noholding lines andno marked leftturn lane.

Figure 19.31 : Poor Intersection Layout




20 SAFETY OF THE ROADSIDE

20.1 Introduction

The first objective in road safety is to keep road users safely on theroad pavement with a reasonable width, a sound road surface, apredictable alignment and good delineation and signs.

However, it must be recognized that drivers and riders are only humanand will sometimes make mistakes and lose control of their vehicles.

The reasons that they might lose control are many, for example:

Excessive speed;

Fatigue or inattention;

Alcohol or drugs; or

Road condition.

Therefore the second objective is to provide a forgiving roadside free ofroadside hazards that may injure the occupants of vehicles that leavethe road and enter the roadside.

A forgiving roadside is more important on the higher speed roadsbecause the severity of a crash with a roadside hazard increasesrapidly with speed.

The importance of a forgiving roadside is emphasized by the studies inmany countries which show that around one in every three fatalities isthe result of a single vehicle running off the road accident.

20.2 Clear Zone

It may be difficult to provide width adjacent to the carriageway that willallow all errant vehicles to recover. Therefore it is generally necessaryto decide on a level of risk management.

The most widely accepted form of risk management for the roadside isthe clear zone concept. The clear zone distance provides a balancebetween recovery area for every errant vehicle, the cost of providingthat area and the probability of an errant vehicle encountering a hazard.

The clear zone should be kept free of non-frangible hazards. Wherethis cannot be achieved, errant vehicles should be protected fromrunning into these hazards by the use of certified roadside safetybarriers. The median of a divided highway will need road safetymedian barriers if hazards exist within the clear zone or if a trafficvolume warrant is demonstrated.




Some typical road environment hazards are:

• Poles;

• Trees;

• Steep side slopes;

• Water courses, dams;• Culvert endwalls;

• Fences and encroaching buildings; and

• Bridge piers and abutments;

The following frangible based facilities can be located within the clearzone:

• Impact absorbent poles;

• Slip base poles and other slip base structures; and

• Frangible posts - steel, aluminum, wooden and concrete.

Other systems include:

• Drivable endwalls; and

• Extended culverts beyond the clear zone.

Research shows that about 85% of vehicles that leave the road at 100kph are able to stop safely or regain control within an area of 9 meterswide measured from the edge of the traffic lane.

Figure 20.1 : Recovery Area (100 kph operating speed, flat cross slope)

The clear zone width depends on the speed that the vehicle is moving.At 60 kph, 85% of vehicles would recover within 3 meters from theedge of the traffic lane.

This clear zone area adjacent to traffic lanes should be kept free offeatures which could be potentially hazardous to the occupants of anout of control vehicle, such as trees or poles.




Source: Roadside Design Guide, American Association of State Highway and TransportationOfficials (AASHTO), 2002.

Figure 20.3 : Clear Zone Calculation




Radius(m)

Design Speed (kph)

60 70 80 90 100 110

900 1.1 1.1 1.1 1.2 1.2 1.2700 1.1 1.1 1.2 1.2 1.2 1.3

600 1.1 1.2 1.2 1.2 1.3 1.4

500 1.1 1.2 1.2 1.3 1.3 1.4

450 1.2 1.2 1.3 1.3 1.4 1.5

400 1.2 1.2 1.3 1.3 1.4 -

350 1.2 1.2 1.3 1.4 1.5 -

300 1.2 1.3 1.4 1.5 1.5 -

250 1.3 1.3 1.4 1.5 - -

200 1.3 1.4 1.5 - - -

150 1.4 1.5 - - - -

100 1.5 - - - - -

Table 20.1 : Curve Correction Factor

Note: The clear zone curve correction factor is applied to the outside of curvesonly. The clear zone distance obtained from Figure 20.3 is multiplied by thecorrection factor. Curves flatter than 900m radius do not require anadjustment.

20.3 New Roads

Achievement of the clear zone is most often economically feasiblewhen a new road is being built or an existing road is undergoing majorreconstruction. For this reason , the provision of a clear zone shouldalways be considered when new works are planned.

20.4 Existing Roads

On the existing road network, particularly in urban areas, it can be verydifficult to achieve a clear zone. In urban areas there are many features

on the roadside like electricity and telephone poles, signs, trees andmany services under the surface like water pipes, drainage, andcables. This usually means there are very few options for relocatingpoles or other hazards.

Therefore, on existing roads it is best to focus on the high risk sitessuch as on tight curves or at the end of long downward slopes and onroads with high operating speeds.




20.5 Treatment of Hazards

The options for treating roadside hazards are:

Remove the hazard.

Move the hazard outside the clear zone.

Figure 20.4 : Relocated Pole

The above pole has been placed as far as possible from the traffic.

Modify the hazard so that it is not so dangerous . For example , installing a cover on an open pit or making the end of a culvertdrivable.

Figure 20.5 : Drivable Culvert End

Drivable culvert ends are designed to enable vehicles to ride overthe hazard. Bars are placed tangential to the flow of traffic to bespaced at not greater than 0.6m center lines. These can be utilizedfor longitudinal drain culverts and cross drain culverts.




Replace the hazard with something that it is not so dangerous, forexample replace steel sign posts with frangible (collapsible) woodenposts

The steel I-beam sign posts in the following photo constitute a roadsafety hazard:

Figure 20.6 : Steel Sign Posts

Frangible wooden posts breakaway if struck by a vehicle and willnot injure occupants:

Figure 20.7 : Frangible Wooden Posts




Another example is roadside poles. They are generally immovableobjects that cause significant damage if struck. In the photo below,the engine has been pushed into the passenger compartment.

Figure 20.8 : Pole Hazard

Specially designed poles are available which absorb the impactand collapse when struck by a vehicle thus protecting theoccupants of a vehicle.

Figure 20.9 : Impact Absorbing Pole




Shield the hazard with a barrier system. Figure 20.10 shows apicture of a roadside hazard with no barriers.

Figure 20.10 : Unprotected Roadside Hazard

Figure 20.11 is an example of how such a hazard could be treated:

Figure 20.11 : Use of Barrier




20.6 Roadside and Median Safety Barriers

Roadside barriers are used to shield errant vehicles from running intohazards that cannot be relocated or made more frangible. The barriersare a hazard in themselves and accordingly should only be used when

they are less of a safety concern than the hazard they are protecting.

Roadside barrier systems maybe considered for use only after theyhave been satisfactorily crash tested, computer simulated or designedby other professionally acceptable methods that demonstrateacceptability to meet the testing regime stated in the Road DesignGuidelines, AASHTO 2002.

The acceptance of roadside safety barrier systems is based on anevaluation of its performance in an idealized crash test (vehicle intracking mode, approach surface 1:10 or flatter, paved and free fromobstructions such as curbs) for a specific weight and type of vehicle atdesignated speeds and impact angles.

In accordance with the National Corporative Highway Research Project350 (NCHRP350) procedures, there are six test levels to provide arange of restraint requirements and impact severity conditions (refer toTable 20.2). The criteria are based on:

• Structural adequacy of the barrier system;

• Occupancy risk and the impact velocity and ride downacceleration limits; and

• Vehicle trajectory after impact.

Table 20.2 : Test Levels for Roadside Barriers




Test level 3 is considered to be the rating by which roadside barriersare designed. They are applicable for cars and pick-up trucks at 100kph with a nominal angle of impact of 20 degrees. The roadwork zonesystems can be designed for test levels 0, 1, 2 and 3 at nominal speedsof 50, 70, and 100 kph respectively, and at 20 degrees nominal angle.

Roadside safety barriers and the equivalent test level category of eachare listed below. The test level rating of a barrier system can beincreased by raising the height of the top of the system and proven byacceptable methods.

20.6.1 Road Safety Barrier Systems:

Flexible Wire Rope Safety Barrier Systems: Test Level

• ‘Brifen’ four (4) wire ropes TL 3

• ‘Flexible’ four (4) wire ropes TL 3

• ‘Armour Wire’ three (3) wire ropes TL 3

Semi Rigid Systems:• W-beam steel barrier TL 3

• Thrie-beam steel barrier TL 3

• Hollow box steel barrier TL 3

Rigid Systems:

• Stone masonry – parkway TL 3

• F-shape concrete barrier TL 4

• Concrete single slope barrier TL 4 to 5

• Vertical face concrete barrier TL 4 to 5• High containment concrete barrier TL 5 to 6

Road Work Systems:

• F-shape concrete barrier TL 3

• Plastic water filled barrier TL 0, 1, 2 & 3

• Truck mounted attenuators TL 3

These road safety barrier systems are detailed in Figures 20.12, 20.13and 20.14.

The systems all have specialized terminals that provide control leddecelerations. Terminals provide deceleration below recommendedlimits and ensure that the vehicle is not speared, vaulted, snagged orrolled on impact. All these criteria combine to provide the necessaryroad safety features of a total system.

Crash cushion systems are also used to shield hazards in confinedlocations, such as the junction of concrete barriers, at ramp gorelocations and other rigid hazards.




Figure 20.12 : Median Barriers




Figure 20.13 : Roadside Barriers




Figure 20.14 : Roadwork Barriers




Concrete barriers are best suited to situations where there is limitedspace between the barrier and the hazard. Typically , this occurs innarrow medians or in areas of restricted road cross section. Thegreatest concern with concrete barriers is the method of termination.Available options include:

• Steel W-beam terminal assembly to shield the end of theconcrete barrier in association with a bridge approachassembly;

• Plastic water filled barrier systems used as terminals;

• Burying the end of the barrier in an adjacent cut face; and

• Shielding the barrier system with an impact attenuator/crashcushion system.

Site characteristics will generally determine the most appropriate typeof termination/attenuation to use.

Concrete barrier systems may be considered on high volume roads asthey retain full functionality after impact, provide excellent whole of life time costs and minimize the risk to workers on roadwork sites.Maintenance of concrete barriers is minimal after impact. It is importantthat on roadwork sites, individual F-shape concrete block barriersystems are adequately and physically connected to each other to forma continuous system of units rather than free standing units. Refer toAppendix 2 Continuous Concrete Barriers.

Steel W-beam barriers are perhaps the most common barrier and areused extensively in urban and rural areas. The effectiveness of W-beam is dependant on its length and offset from the traveled way. W-beam termination also needs to meet appropriate standards. TheBreakaway Cable Terminals (BCT) are detailed on standard drawingsin Appendix 1 - Roadside Barriers Standard Drawings. Standarddrawings are available for the approach end terminal SD 3541 (BCTA)and the departure end SD 3542 (BCTB). The cable tensions thesystem over the first and last 30m of installation. Parallel and flaredsystems can be designed and these systems are included in thestandard drawings in Appendix 1.

Wire rope safety barrier systems work through high tension cables. Anerrant vehicle deflects the wire ropes, the supporting posts bend andthe vehicle is redirected back towards the direction of travel. Wire ropebarriers are the most forgiving of the barrier systems. However, due tothe deflection of the wire ropes, consideration of the offset to featuresbehind the barrier is very important.

The minimum offset of the barrier systems from the edge of the trafficlane are detailed in Table 20.3. The deflections of the various systemsare detailed in Table 20.4. In design, the consideration of the locationof the barrier systems and the offset to the face of the hazard, are thefirst steps in designing a system.




Table 20.3 : Offset from edge of traffic lane to face of barrier

Description Offset (m)

Minimum offset 1.50

Minimum offset without DPWH, Director,Bureau of Design approval. 1.00Absolute minimum offset with DPWH,Director, Bureau of Design approval. 0.60

Table 20.4 : Clearance from face of barrier to face of hazard

Barrier Type Deflection (m)

Wire Rope Safety Barrier

2.40 to 3.20m post spacings 2.00

1.20m post spacings 1.50

1.00m post spacings 1.30

Blocked Out Steel W-Beam

2.50m post spacing 1.00

1.25m post spacing 0.75

Concrete Barriers

All types 0.10

Location of Curb Adjacent to Barriers

The location of safety barriers in the vicinity of curb and gutter is to beconsidered carefully. If curb and gutter is essential in high speedlocations, the face of curb should be located:

• At least 3m from the face of concrete safety barriers;

• At least 3m from W-beam and wire rope safety barriers for

concrete barrier curb;• At least 3.0m from W-beam safety barrier or wire rope safety

barrier for concrete mountable / drop curb & gutter; and

• In areas where the operating speed is less than 70 kph , anoffset of 0.2 to 0.3m can be tolerated to minimize damage tovehicles.




The use of concrete mountable / drop curb & gutter in conjunction withsafety barrier systems is preferable to using concrete barrier curb andgutters as the drop curb minimizes resultant dynamic jump of vehicles.

Roadwork Safety Barriers

Roadwork barrier systems come in various forms and can be precastconcrete with impact attenuators/crash cushion terminals or water filledplastic systems. These systems must be considered during the designphase of a project. Truck mounted attenuators can be used for shortterm or mobile roadwork or pavement marking works.

20.6.2 Design Of Barrier System Installations

The design of road safety barrier systems should take into account thefollowing considerations:

• Location – topography;

• Clear zone (Cz);

• Warrant;• Runout length (LR);

• Length of need (X);

• Offset from edge of traffic lane to face of barrier;

• Clearance from face of barrier to face of hazard;

• Ground approach slope to the barrier;

• Flare rate;

• Transition lengths from barrier to barrier system type; and

• End terminals.

The following steps provide guidance in the design process:

STEP 1. CLEAR ZONE

The design of clear zone width for the various criteria of design speed,ADT exposed to the hazard (ADT/2), fore slope and back slope (fill andcut) is determined using Figure 20.3.

The clear zone width should be increased on the outside of curvesusing the curve factor shown on Table 20.1.

A further factor in the determination of clear zone is the consideration ofthe steepness of the slope of fill. In this case an effective clear zonewidth needs to be calculated. As the slope becomes steeper, the abilityof a vehicle to recover back to the traveled way reduces. This resultsstatistically in only a proportion of the slope width being available asclear zone. The variations of effective clear zone can be calculatedusing Figure 20.15.




Figure 20.15 : Effective Clear Zone (ECZ)




STEP 2. WARRANT

The warrant for barrier systems can be determined by a riskassessment taking into account the various issues (refer to Section 21Risk Assessment).

The warrant for the use of safety barriers can be establishedconsidering:

• Fore slope or back slope steepness and height;

• Unforgiving hazards within the clear zone; and

• Water hazards within the clear zone.

The warrant for roadside safety barriers on fill slope can be determinedby reference to Figure 20.16. The warrant is based on fill height andslope.

The warrant for median safety barriers is determined by using Figure20.17. This warrant is based on the width of the median and the ADT.

In both the fill slope and median considerations, a warrant to install abarrier system may also be determined by accident blackspotinvestigations if traffic accidents indicate that a barrier would reduce theseverity of accidents.

Figure 20.16 : Fill Slope Safety Barrier Warrant




Figure 20.17 : Median Safety Barrier Warrant

STEP 3. RUNOUT LENGTH & TRIANGLE

The statistical length over which a vehicle leaves the edge of trafficlane to come to rest is the runout length for errant vehicles. The lengthis determined by using Table 20.5 considering ADT and design speed.The runout triangle can then be plotted by using the appropriate runoutlength and the protected width SDs 3521 & 3531, the clear zone widthor effective clear zone width.

Refer to Figures 20.18 and 20.19 for detailed descriptions of the runouttriangle for the approach barrier and departure / opposing barrierlengths.

For hazards located within the clear zone width, the roadside barriersystems can be designed using SD 3521 and SD 3531. The protectedwidth can be applied to each layout type using the tabulations shown.




Table 20.5 : Runout Lengths for Barrier Design

ADT Over 6000 2000-6000 800-2000 Under 800

DesignSpeed

(kph)

RunoutLength

(m)

RunoutLength

(m)

RunoutLength

(m)

RunoutLength

(m)110 145 135 120 110

100 130 120 105 100

90 110 105 95 85

80 100 90 80 75

70 80 75 65 60

60 70 60 55 50

50 50 50 45 40

Figure 20.18 : Approach Barrier Design Elements

Figure 20.19 : Departure / Opposing Barrier Design Elements




STEP 4. OFFSET & CLEARANCE

The offset from the edge of the traffic lane to the face of barrier needsto be established. The barrier should be located as far as possiblefrom the face of the barrier. The minimum offsets are shown in Table20.3. Adjacent to fill slopes, the offset to the face of barriers canextend to within 1.0m of the hinge point of the fill slope for W-beambarrier and wire rope safety barrier systems respectively.

The location of the barrier in front of a hazard requires consideration ofthe minimum clearance from the face of the barrier to the face of thehazard being protected. The minimum clearances are shown in Table20.4 for the various types of barrier systems.

STEP 5. LENGTH OF NEED

The length of need (X) is the length over which a barrier is needed tostatistically protect a vehicle from running into a hazard that would haveworse results than running into a barrier. The length of need is thelength of barrier that falls within the runout triangle.

STEP 6. BARRIER TERMINALS

Barrier terminals are needed to transition from no barrier to the fullbarrier system. Position the end terminals outside the runout triangle.The breakaway cable terminal to be used for W-beam is detailed in thestandard drawings. Concrete barrier system terminals can be designedusing W-beam or Thrie beam lengths suitably flared or tapered awayfrom approaching traffic. Wire rope safety barriers can also be usedand plastic water filled barriers may be used as terminals for worksiteterminal treatments. Refer to the standard drawings for more detail.For other barrier systems, the manufacturers will provide detaileddrawings of their certified terminal details.

STEP 7. FLARE RATE

A further consideration is to flare the barrier systems away from thetraveled way. The flared barrier is used when terminating a systembeyond the clear zone width. Maximum flare rates for barrier systemsare shown in Table 20.6. A flared barrier system is detailed on SD3511 in Appendix 1. When designing flared barriers the flare ratesmust be kept within the maximum values to ensure any impact angle isacceptable.




Table 20.6 : Maximum Flare Rates for Barrier Design

Design Speed

(kph)

Flare Rate

Rigid Barrier Systems

Flare RateSemi- Rigid and

Flexible Barrier Systems110 20:1 15:1

100 18:1 14:1

90 16:1 12;1

80 14:1 11:1

70 12:1 10:1

60 10:1 8:1

50 8:1 7:1

STEP 8. TRANSITIONS

A transition section should always be designed when changing fromone barrier system to another. This provision builds in a gradualchange between the two systems against which an errant vehicle wouldtransition itself gradually as it runs along the face of the transition. Thetransition does not allow entrapment or pocketing of the errant vehicle.A bridge transition section is detailed on SD 3081 Appendix 1.

STEP 9. GROUND APPROACH SLOPE

The slope of the ground on the approach to the barrier system shouldbe designed as 1:10 or flatter. When retrofitting an existing highway aground slope of 1:6 will be tolerated.




20.7 Further Examples of Barrier Installations

Further examples of good and poor practice with regard to roadsidehazards are shown below.

20.7.1 Bridge Railing

The picture shows that there is a steep drop off at a bridge with poorrailing and no approach barrier system.

Figure 20.20 : Poor Bridge Railing

A good treatment would be to install a strong bridge railing with abarrier treatment on the approach similar to the following.

Figure 20.21 : Very Good Bridge Railing




20.7.2 Connection to Bridge Railing

There is a large gap between the steel railing and the concrete bridgewall in the following photo. If a vehicle hit the steel railing it woulddeflect and the vehicle would almost certainly strike the end of theconcrete wall with dire consequences.

Figure 20.22 : Poor Bridge Railing – No Connection

The following picture shows how two different railings should beoverlapped to prevent the possibility of a vehicle striking the end of thesecond railing.

Figure 20.23 : Good Connection to Bridge Railing




20.7.3 Railing End Treatment

Figure 20.24 : Poor End Treatment

The above end treatment can result in a vehicle being speared. Aphotograph showing this in a real traffic accident is in Figure 20.25.

Figure 20.25 : Car Speared by Guardrail




The following photograph in Figure 20.26 is an example of a certifiedtreatment with a break away terminal (BCT) at the end of steelguardrail.

Figure 20.26 : Very Good End Treatment

20.7.4 Unconnected Concrete Barriers

Unconnected concrete barriers of the kind shown in the following photoare dangerous because a vehicle which is out of control is very likely toend up in the space between two barriers and then the effect could besimilar to hitting the end of such barrier.

Figure 20.27 : Unconnected Concrete Barriers




To make such barriers effective, they should be properly connectedwith the space between them less than 100mm. Refer to Appendix 2.

Figure 20.28 : Good Connected Barriers

The following is another example of a concrete barrier that is properlyconnected.

Figure 20.29 : Very Good Connected Barrier




Any barrier can be dangerous if it is unconnected and the ends are nottreated correctly.

In Figure 20.30, a vehicle could potentially become snagged if it hit just

prior to the discontinuity.

Figure 20.30 : Poor Unconnected Barrier

20.7.5 Gore Area

A barrier will often begin where there is a split in the road , like where anoff-ramp leaves the freeway thus forming a gore. The following goretreatment is very hazardous.

Figure 20.31 : Poor Gore Treatment




Figure 20.32 : Poor Gore Treatment

Figure 20.33 shows a much safer treatment using a system that collapses instages if a vehicle hits it.

Figure 20.33 : Very Good Gore End Treatment using Impact Attenuator




20.7.6 Trees

Trees are often planted for street beautification reasons but can bepotentially dangerous roadside hazards.

Figure 20.34 : Tree Hazard

20.7.7 Street Lighting Poles

Roadside street lighting poles in a median or roadside areas can posea major hazard to motorists.

Solid or rigid street lighting poles can be specified or converted toimpact absorbing poles or to slip based poles that are frangible. Theseare shown in Figure 20.35.

Slip Base Pole Impact Absorbing Pole

Figure 20.35 : Frangible Poles




The slip-base pole is designed to break away at the base when avehicle collides with it. There are special electrical connections whichalso breakaway. This type of pole can often be reused after a collision.This type of pole is mostly suitable for locations where the speeds aregreater than 60 kph and is the preferred treatment.

Impact-absorbing poles do not break away but yield progressively,generally embracing and entrapping the vehicle. They are suited tolocations where it is undesirable for the pole to fall to the ground suchas high pedestrian areas or where the median or island is narrow andtraffic is heavy.

The specification and standard drawings for these poles are inAppendix 3.

Figure 20.36 : Impact-Absorbing Pole

Figure 20.36 illustrates how impact absorbing poles perform in a crash.

The diagrams in Figure 20.37 shows the different modes of behaviorwhen a vehicle hits a slip base or impact absorbent pole.

Other utility poles used for electricity supply may also be hazardous.These cannot be converted to frangible poles. However, a safetybarrier may need to be considered for individual poles in hazardouslocations to protect occupants of an errant vehicle.




Figure 20.37 : Impact Behavior - Slip Base and Impact Absorbing Poles




20.7.8 Other Examples of Roadside Hazards

It is important to consider roadside safety issues when managing aroadworks site. The worksite in Figure 20.38 has a deep excavationwhere a stronger more effective safety barrier should have beeninstalled.

Figure 20.38 : Hazardous Roadwork Site

The pipe installation in Figure 20.39 is hazardous. The pipe could havebeen redirected behind the bridge barrier and supported on brackets

cantilevered off the outside of the bridge. Alternatively, the guardrailcould have been relocated to shield the pipe installation.

Figure 20.39 : Hazardous Pipe Installation




20.7.9 Curbs in Front of Barriers

Careful consideration must be given when placing curbs in front of abarrier as shown in Figure 20.43. A curb that is just in front of a barriercan have the effect of lifting the impacting vehicle. If struck at highspeed in certain circumstances the curb may cause the vehicle tobounce over the barrier. Section 20.6.1 provides guidance relating tocurbs adjacent to safety barriers.

Figure 20.43 : Curb in front of Barrier




RISK ASSESSMENT




21 RISK ASSESSMENT

A risk assessment strategy may assist in determining priorities for actionwhen considering design options or decisions that may have safetyimplications. In addition, when a road safety audit report contains safetyconcerns, the Project Engineer or designer may use a risk assessmentapproach to help to determine a response to those concerns. The followingrisk assessment process is the suggested method to be used. The followingtables provide an indication of the level of risk and how to respond.Determine into which category in Table 21.1 and 21.2 the safety issue bestfits. From this select the risk category in Table 21.3 and its suggestedtreatment priority in Table 21.4. This system does require the application ofprofessional judgment at each step.

21.1 Risk

Risk can be defined as the combination of the likelihood and theconsequence of a crash occurring.

21.2 Likelihood

The likelihood of a crash occurring depends on various factors like driverbehavior (inattention, fatigue, risk taking), the quality of the road (surface,alignment etc) and the vehicle (poorly maintained brakes, tires etc.). Thelikelihood that a given type of crash might occur can be defined in accordancewith the following table:

Frequency DescriptionFrequent One or more times per month

Occasional More than once per year (but less than12)

Infrequent Less than once per year

Table 21.2 : Likelihood Definition

21.3 Consequence

If a crash does occur, the consequence of the crash depends on things likethe speed of the vehicle, the severity of roadside hazards and the ability ofthe vehicle to protect the occupants (seatbelts, air bags, crumple zone,collapsible steering column , etc). The consequences can be defined inaccordance with the following table :



Severity of anaccident

Description

Very Serious Multiple fatalities, severe injuries

Serious Single fatality, severe injuries

Minor Minor injuries, property damage

Table 21.3 : Consequence Definition

21.4 Risk Category

The risk is then estimated from the likelihood and consequence scores inaccordance with the following table :

Consequence

VerySerious

Serious Minor

LikelihoodFrequent HIGH HIGH MEDIUM

Occasional HIGH MEDIUM LOWInfrequent MEDIUM LOW LOW

Table 21.4 : Risk Category

revised road safety design manual - june 1, 2011

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