Highway Engineering

Highway Engineering 2015

1. PART A1.1 History of roads in Bhutana) Construction of first motorable road from Phuentsholing to ThimphuPrior to 1962 Bhutan was connected only by footpaths and mule tracks. Construction of Bhutans first road from Phuentsholing to Thimphu started in earnest by Bhutan Engineering Services in 1958.The project was later completed by Project DANTAK in 1962.With the completion of the motorable road from Phuentsholing to Thimphu in 1962 journey from Thimphu to Phuentsholing which took upto to 6 days on foot was reduced to only about 6 hours by motor vehicle.

b) Construction of Samdrup Jongkhar to Trashigang and Trongsa to GelephuConstruction of Trashigang Samdrup Jongkhar began in 1961.The extremely hostile terrain of Eastern Bhutan did not deter the men and officers of Project DANTAK and the project was completed in 1968. The legendary Melong Brak near Narphung is history.By early 1980s Project DANTAK completed laying the main trunk roads which included Samdrup Jongkhar-Trashigang road in Eastern Bhutan, Trongsa Gelephu road in central Bhutan and the 546 km lateral road from Thimphu to Trashigang.

1.2 Types of Roads in BhutanThe concise 2009 document on road classification in Bhutan introduced a new classification of roads for the country. This super cedes the classification given in the Road Act of 2004. The new classification was codified in the Road Bill of 2012. As described by the 2009 guidelines, the new road classification has five categories National highways District roads Farm roads Thromde roads Access roads

Government polices and acts relating to road construction

1.3Government Plicies and ActsAs per Road Act of the Kingdom of Bhutan, 2004.Powers of the GovernmentThe Royal Government shall exercise the following powers, with regard to roads:1. approve long term master plans for roads and Five Year Plans;2. approve policies regarding the general system for lease of roads andbridges to legal entities or to persons;3. approve policies regarding the construction of toll roads and bridges.

Powers of the MinistryThe Ministry shall exercise the following powers with regard to road, -1. formulate policies with regard to the national road network;2. develop and implement long term master plan for national road networkand Five Year Plans;3. develop, coordinate and organise the implementation of road regulationsincluding road user charges and approve rules regarding such matters;4. approve standards for the road construction, maintenance works andregulations regarding the control, management and use of roads;5. develop and implement policies for the promotion of the private road, construction industry, and provide for the maintenance of uniformstandards and quality in that industry;6. develop and implement policies, subject to Governments approval the7. lease of roads to legal entities or to persons and individuals;develop and implement policies for the construction of toll roads andbridges based on regulations established under this Act;8. determine and approve toll rates;9. designate international roads in accordance to the Governmentsapproved bilateral and multilateral treaties, agreements and based on theclassifications and proposals of the Department.

Furthermore powers and functions of other road agencies which includes DzongkhagYargayTshogdu and Dzongkhag Administration has power to formulate ans approve dzongkhag level plans for the construction and maintenance of roads.

1.4 Construction approaches.Traditional road constructionSteps involved in traditional construction are: Planning The first step in any road construction and maintenance project is properly planning and evaluating the needs it is intended to serve. Local traffic patterns, both current and future should be studied, and a cost-benefit analysis should be performed. Design The next phase in a typical construction and maintenance project is the design. Surveyors will physically visit the site and use laser technology to pinpoint the alignment, shape, and direction of the road. Location, terrain and soil properties, potential water access and drainage issues, and the potential for future expansion in the immediate physical vicinity are all addressed during this portion of the project, as well as potential impact on nearby residents, if any. Earthworks The earthworks are the first step that most people would recognize as part of a road construction and maintenance project on sight. The intent of this step is to provide a firm and stable foundation. If the earthworks are not executed correctly, the road surface will definitely experience premature failure at some point. Embankments, leveling, fill, compacting, drainage and sewers are all installed and inspected before the project continues. Laying Pavement Most modernroad construction and maintenanceprojects employ either asphalt or concrete for this purpose, though this is slowly changing as organizations realize the benefits of alternative solutions such as those offered by Global Road Technology. The physical surface of the road is created, smoothed, and trimmed off to the appropriate level, then sealed, connected, and reinforced to prevent cracks in the future. QC After the surface is successfully constructed, typically another battery of quality control tests will be performed to close out the road construction and maintenance project before it is truly considered finished. Drainage will be checked again, grading levels, landscaping and rehabilitation, and everything else. If all tests get positive results, the road can be opened and is ready to use. Maintenance Over time, traffic and environmental effects will damage traditional road surfaces, which require rehabilitation.

Environmentally Friendly Road Construction in BhutanEnvironmentally friendly design takes into account specific site conditions such as geologically sensitive areas, wet areas, rocks, paddy fields and areas with high environmental and cultural value, to prevent and mitigate environmental damages, as much as possible. Such important site conditions are first identified through a desk based study. The desk based study uses accurate maps (1:5,000) and aerial photograph interpretation to identify the geologically-hazardous and environmentally and culturally vulnerable areas. These areas are marked on the map after which the alternative road networks and road alignments can be plotted to design a low-cost road network with an aslarge as possible area serviced by the network. The desk based study is followed by a feasibility study and an environmental impact assessment (EIA), which includes social, ecological, technical and economic aspects. The proposed road alignments must also be verified in the field from an economic, technical, social, geological and environmental point of view. Therefore the Department of Roads survey team collaborates with theEnvironmental Assessment team and when necessary with a team of the Department of Geology and Mines to identify the best possible alignment.

Cycle of this process is mentioned below.

EFRC equipment and labour basedEnvironmentally friendly design takes into account specific site conditions such asgeologically sensitive areas, wet areas, rocks, paddy fields and areas with highenvironmental and cultural value, to prevent and mitigate environmental damages, asmuch as possible. Such important site conditions are first identified through a desk basedstudy. The desk based study uses accurate maps (1:5,000) and aerial photographinterpretation to identify the geologically-hazardous and environmentally and culturally vulnerable areas. These areas are marked on the map after which the alternative road networks and road alignments can be plotted to design a low-cost road network with as large as possible area serviced by the network. The desk based study is followed by a feasibility study and an environmental impact assessment (EIA), which includes social, ecological, technical and economic aspects. The proposed road alignments must also be verified in the field from an economic, technical, social, geological and environmental point of view. Therefore the Department of Roads survey team collaborates with the Environmental Assessment team and when necessary with a team of the Department of Geology and Mines to identify the best possible alignment.

2. PART B

2.1 Vertical alignment The vertical alignment of a road consists of gradients(straight lines in a vertical plane) and vertical curves. The vertical alignment is usually drawn as a pro_le, which is a graph with elevation as vertical axis and the horizontal distance along the centre line of the road as the the horizontal axis. Just as a circular curve is used to connect horizontal straight stretches of road, vertical curves connect two gradients. When these two curves meet, they form either convex or concave. The former is called a summit curve, while the latter is called a valley curve.

Vertical curves or grade changes, like horizontal curves, requires proper consideration to minimize earthwork, cost, and erosion damage. Vertical curves provide the transition between an incoming grde and outgoing grade.2.2 Gradient vertical curvesA parabolic curve that is applied to make a smooth and safe transition between two grades on a roadway or a highway.

2.3 Design of intersectionsAn intersection is the junctionat grade (that is to say, on the same level) of two or more roads either meeting or crossing. An intersection may be three-way (a T junction or Y junction the latter also known as a fork), four-way (a crossroads), or have five or more arms.At the intersection there are through, turning and crossing traffics and these traffics movements may be handled in different ways depending on the type of intersection and its design.The efficiency, safety, speed, cost of operation and capacity of road system very much depend on the intersection design.Intersection may be classified into two broad groups:1. Intersection at grade : These include all roads which meet at more or less the same level. The traffic manoeuvres like merging, diverging and crossing are involved in the intersection of grade.2. Grade separated intersection: The intersecting roads are separated by the difference in level, thus eliminating the crossing manoeuvres. Some of the traffic factors to be considered in intersection design are relative speed and manoeuvre areas.Manoeuvres areas are those are where, in actual manoeuvre, there is potential collision and also those like channels of approach and departure where the manoeuvre is influenced. Elemental manoeuvre area are those formed by only two single one way lane of flows when they diverge, merge or cross. Multiple manoeuvre area where more than two one lane one way flows are present, traffic operation are much more complex and hence are to avoided in intersection design.2.4 Intersection at GradeAll roads and intersections which meet at about the same level allowing traffic manoeuvres like merging, diverging, crossing, and weaving are called intersection at grade.The basic requirements of intersection at grade are:I. At the intersection the area of conflict should be small as possibleII. The relative speed and particularly the angle of approach of vehicle should be small.III. Adequate visibility should be available for vehicle approaching the intersection.IV. Sudden change of path should be avoided.V. Geometric feature like turning radius and width of pavement should be adequately provided.VI. Proper sign should be provided on the road approaching intersection to warn the driver.VII. Good lighting at night is desirable. VIII. If the number of pedestrians and cyclist are large, separate provision should be made for the their safe passage in the intersection with high volume of fast moving traffic. The various forms of intersection are shown below;

TEE CROSS STAGGERED

SKEWED SKEWED CROSS SKEWED STAGGERED

WYE MULTIPLE

2.4 Rotary intersectionA rotary intersection or traffic rotary is an enlarged road intersection where all converging vehicles are forced to move round a large central island in one direction (clock wise direction) before they can weave out of traffic flow into their respective direction radiating from the central island. The main objective of providing a rotary is to eliminate the necessity of stopping even for crossing stream of vehicle and to reduce the area of conflict. The figure is provided below.

3. PART C3.1 Rectangular or Block pattern:In this pattern, the whole area is divided into rectangular blocks of plots, with streets intersecting at right angles. The main road which passes through the center of the area should be sufficiently wide and other branch roads may be comparatively narrow. The main road is provided a direct approach to outside the city.Advantages: The rectangular plots may be further divided into small rectangular blocks for construction of buildings placed back to back, having roads on their front. In this pattern has been adopted for the city roads. The construction and maintenance of roads of this pattern is comparatively easier.Limitations:This pattern is not very much convenient because at the intersections, the vehicles face eachother.

Rectangular or Block pattern3.2 Radial or Star and block Pattern:In this pattern, the entire area is divided into a network of roads radiating from the business outwardly. In between radiating main roads, the built-up area may be planned with rectangular block.

Advantage: Reduces level of congestion at the primary bottleneck location. Prevents traffic from accessing local flow routes in the direction of the event venue that operate in favor of egress traffic flow. If one is block then other side traffic can move. Vehicles face each other less than block pattern.

Limitations: Proves particularly effective if two-lane ramp traffic does not have to merge at downstream end of ramp. Safety appurtenances such as guide rail transitions, crash attenuators, and post support bases have not been designed to provide adequate protection at hazardous locations from the opposite direction of travel.

Radial or Star and block Pattern3.3 Radial or Star and Circular Pattern:In this system, the main radial roads radiating from central business area are connected together with concentric roads. In these areas, boundary by adjacent radial roads and corresponding circular roads, the built-up area is planned with a curved block system.

Advantages: At traditional intersections with stop signs or traffic signals, some of the most common types of crashes are right-angle, left-turn, and head-on collisions. These types of collisions can be severe because vehicles may be traveling through the intersection at high speeds. With circular pattern, these types of potentially serious crashes essentially are eliminated because vehicles travel in the same direction. Installing circular pattern in place of traffic signals can also reduce the likelihood of rear-end crashes. Removing the reason for drivers to speed up as they approach green lights and by reducing abrupt stops at red lights. Because roundabouts improve the efficiency of traffic flow, they also reduce vehicle emissions and fuel consumption.

Limitations: Center lines of roads leading to circular pattern should be properly aligned with the central island. Approach roads should be sufficiently curved, far enough in advance of circular pattern, to reduce vehicle speeds of entering drivers. Islands separating the approach and exit lanes, known as splitter islands, should extend far enough to provide pedestrian refuge and to delineate the roundabout. Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they are approaching a roundabout and that they should reduce their travel speed. For older drivers declines in vision, hearing, and cognitive functions, as well as physical impairments, may affect some older adults' driving ability. Intersections can be especially challenging for older drivers.

Radial or star and circular pattern

3.4 Radial or Star and Grid Pattern :Change in direction, and because street patterns are the most enduring physical element of any layout, it could potentially contribute to systematic site planning and, consequently, deserves a closer look. Though the network is entirely interconnected, north-south movement becomes circuitous, indirect, and inconvenient, making driving an unlikely choice and vividly illustrating that interconnectedness by itself is insufficient to facilitate movement.

Advantages: Keep vehicular traffic safe with a high proportion of 3-way intersections. Reduce cut-through traffic by similar or other means. Improve traffic flow in both directions using Savannahs cellular structure. Improve land use efficiency and unit density.

Limitations: Islands separating the approach and exit lanes, known as splitter islands, should extend far enough. Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they should reduce their travel speed.

Radial or star and grid pattern

Hexagonal Pattern :In this pattern, the entire area is provided with a network of roads formatting hexagonal figures. At each corner of the hexagon, three roads meet the built-up area boundary by the sides of the hexagons is further divided in suitable sizes.

Advantages: Three roads meet the built-up area boundary by the sides of the hexagons.

Limitations: Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they should reduce their travel speed.

Hexagonal Pattern

3.5 Minimum Travel Pattern :In this road pattern, city is contented by sector center, suburban center and neighborhood center by the road which required minimum to connect the city center.

Advantages: These types of potentially serious crashes essentially are eliminated.

Limitations: Traffic signs, pavement markings, and lighting should be adequate so that drivers are aware that they should reduce their travel speed. Intersections can be especially challenging for older drivers.References:Bhutan: Transport System,(1998). Retrieved from http://www.photius.com/countries/bhutan/economy/bhutan_economy_transportation_and_c~313.htmlKhanna, S.K., Justo,C.E.G.(2011), Highway Engineering,(9th ed.). India: Roorkee Press.Road Act of the Kingdom of Bhutan, (2004), Retrieved from http://www.nab.gov.bt/en/business/actsShalik,(April,2012).Road Pattern used in Highway Planning, Retrieved from http://engrshakil.blogspot.com/2012/04/road-patterns-uses-in-highway-planning.html

Tenzin Wangchuk [EDC2012061]14