04 ce 122 traffic characteristics

8/13/2019 04 CE 122 Traffic Characteristics

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School of CE-ENSEMapua Institute of Technology (MIT)


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Human factors (Road Users) Drivers

Passengers

Pedestrians

Cyclists

Vendors

Vehicle characteristics

Traffic Flow/Roadway Environment


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Design Driverrange of drivers whose abilities and limitations should be takeninto account in designing roads, vehicles, traffic control devices,road maps and other aids to control, guidance and navigation

Perception-Reaction TimeHow quickly a driver can respond to a situationInterval between the appearance of some object or condition inthe drivers field of view and the initiation of a responsePRT= 2.5 seconds used for design standards by the AmericanAssociation of State Highway and Transportation Officials (AASHTO)1.5 seconds for perception and 1.0 seconds for making theresponse

Information Processing and Perception


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Perception-Reaction Time Process

Perception the driver sees a control device, warning sign, orobject on the road

Identification the driver identifies the object or controldevice and thus understands the stimulus

Emotion the driver decides what action to take in responseto the stimulus, ex. To step on the brake pedal

Reaction or volition the driver actually executes the actiondecided on during emotion subprocess.


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Visual Acuity ability to see fine details of an object Peripheral Vision ability of people to see objects beyond the cone of

clearest vision

Color Vision ability to differentiate one color from another.

Glare Vision and Recovery There are 2 types of glare vision: direct andspecular. Direct Glare occurs when relatively bright light appears in theindividual field of vision and specular glare occurs when the image reflectedby the relatively bright light appears in the peripheral field of vision. Both ofthem results in a decrease of visibility and cause discomfort to the eye

Depth Perception Affects the ability of a person to estimate speed anddistance. It is important on 2-lane highways during passing maneuvers,whenhead-on collision may result from lack of proper judgment of speed anddistance.

Central SightField

RightPeripheralSight Field

LeftPeripheralSight Field

V(kph) (degrees)

40 30

60 21

80 14

100 10


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length of roadway ahead that is continuously visible to thedriver

depends on the vehicle speed, vehicle size and driver PRT

minimum sight distance available should be sufficiently long

enough to enable a vehicle traveling at the design speed tostop before reaching a stationary object in its path (AASHTO)

Sight Distance

Important elements in Sight Distance

Stopping Sight Distance Decision Sight Distance

Passing Sight Distance

Intersection Sight Distance

Human Characteristics - Driver


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Time of day

Fatigue

Alcohol and drugs

AgeGender differences

Social factors

Motivation

Risk taking and risk perception

Emotions and stress

Personality

Behavioral compensation or adaptation

Other Factors Affecting the Driver



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Perception-Brake Reaction Times for Various Percentiles of Driving Population (SSD, sec)Source: Gordon et al (1984)

Percentile of DriversElements 50 75 85 90 95 100

PERCEPTION

Latency 0.24 0.27 0.31 0.33 0.35 0.45

Eye Movement 0.09 0.09 0.09 0.09 0.09 0.09

Fixation 0.20 0.20 0.20 0.20 0.20 0.20

Recognition 0.40 0.45 0.50 0.55 0.60 0.65

DECISION 0.50 0.75 0.85 0.90 0.95 1.00

BRAKE REACTION 0.85 1.11 1.24 1.42 1.63 2.16

TOTAL 2.30 2.90 3.20 3.50 3.80 3.90

Design Driver Characteristics:85thto 95thpercentile range (for safety purposes)50thpercentile value (absolute minimum value for design)



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The need to move both vehicles and pedestriansand safety at the same locations presents asignificant challenge to the traffic engineerbecause the design of roadways emphasizes

movement of motor vehicles.

Pedestrian access such as crosswalks andwalkways is often missing or inadequate in many

roads and traffic generators such as malls.

Human Characteristics - Pedestrians


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Body area (source: AASHTO)

area of the body approximated

by an ellipse

0.60 m wide and 0.50 m deep

Mean Walking Speed =

73.15 m/min. (4.4 km/hr) (AASHTO, 1984)

70.65 meters/min. (4.2 km/hr) (Filipino pedestrian)

0.50 m

0.60 m shoulder breadth

body

depth


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a.)Pedestrian Walking Speeds (PWS):Free flow = 0.6 1.8m/s (2-6fps)Mean = 1.2 1.4m/s (4-4.5fps)

= 0.9m/s (3.0fps) with large no. of elderly pedestrians(AASHTO)

Pedestrian traffic signals = 4.0fps

PWS = 143mm/minute (7.8fps) construed as runningFastest movement afoot is 10m/s (33fps)

b) Flow Rate:LOS A Free Flow = 7 or less Pedestrians/min./ftLOS E @ Capacity = 20-25 Pedestrians/min/ftLOS F Below Capacity = />25 Pedestrians/min/ft

c) Density:LOS A Free Flow = 35 ft2/PedestrianLOS E @ Capacity = 5-10 ft2/PedestrianLOS F Jam Capacity = 5 ft2 or less/Pedestrian

(@ 2 ft2/Pedestrian, nobody can move anymore)


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Condition Maximum

Tolerable

Distance(m)

Walking

Distance time

(min.)

Covered Walkway 1,500 20

Pavement with Shade 750 10

Without protectionfrom the elements

375 5

Very poor environment 180 2

* Average walking distance of Filipinos is 215 m Source: G.P. Guerilla


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Country m/min

New York, USA 81

London, England 79Israel 79

Singapore 74

Thailand 73

China 72

Metro Manila, Philippine 70.65


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1. Safety-security of the walking area guardrail/fence lighting security guard/police pedestrian signals height difference between street and sidewalk marking separation between street and sidewalk

2. Convenience-attractiveness of the walking area presence of shops

surface conditions

Width

3. Comfortability-environmental and climaticconditions presence of trees/shrubs

air quality

noise quality


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4. Continuity-walking flow of pedestrians

presence of vendors presence of street furniture

pedestrian-car conflict

5. System coherence

architectural and cohesive design of the facility to the buildings

relates to the clear orientation of the user of the facility within the area

information signs

perception of space

landmark

6. Level of congestion-space requirement and LOS of thefacility

space requirement suitable for circulation and other activities


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Important - vehicle fits the driver Static (weight & dimensions, features) & dynamic

characteristics (power, acceleration, deceleration)

Different Vehicle type i.e. car, bus, truck, etc.

DESIGN VEHICLE

Selected motor vehicle with dimensions &/or operatingcharacteristic of such a critical nature that they influenceor control the design & operation of the highway

Most important is the minimum turning radius Depending on the road classification, proportions on the

various types & sizes of vehicles expected to use thefacility


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Heavier vehicles like trucks have lower rate of acceleration thanpassenger car

Heavy vehicles at a signalized intersection will delay allpassenger cars behind it as it accelerated from a stop

Gaps will form in front of the heavy vehicle

Trucks occupy morespace: length and gap

Vehicle Characteristics


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occurs automatically when the accelerator pedal is releasedbecause of the retarding effect of the resistance to motion,including engine compression forces

for controlled deceleration, vehicle brakes are used to restrain

vehicle motion

Deceleration Performance

maximum rates are used for estimating minimum stopping

distances in emergencies

the time required to stop a vehicle is a primary considerationin almost every aspect of traffic system design and operation

Deceleration with Brakes or Braking Performance

Vehicle Characteristics


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ESIGN VEHICLE TYPE SYMBOL

Overall Overhang

Height Width Length Front Rear WB1 WB2 S T WB3

ssenger carngle-unit truckngle-unit bus

ticulated busombination trucksIntermediate semitrailerLarge semitrailerDouble Bottom

Semitrailer-full trailerInterstate Semi-Trailer

Interstate Semi-Trailer

PSUBUS

A-BUS

WB-12WB-15WB-18

WB-19*

WB-20+

1.34.14.1

3.2

4.14.14.1

4.1

4.1

2.12.62.6

2.6

2.62.62.6

2.6

2.6

5.89.1

12.1

18.3

15.216.719.9

21.0

22.5

0.91.22.1

2.6

1.20.90.6

1.2

1.2

1.51.82.4

2.9

1.80.60.9

0.9

0.9

3.46.17.6

5.5

4.06.13.0

6.1

6.1

8.29.16.1

12.8

14.3

1.2

1.2

6.1

1.6 6.4

WB1, WB2, WB3 =effective wheel basesS =distance from rear effective axle to the hitch pointT =dist. from the hitch point to the lead effective axle of the

following unit* =design vehicle with 14.6m trailer as adopted in 1982 STAA+ =design vehicle with 16.2m trailer as grandfathered in 1982 STAA

Typical Vehicle Classes and Their BasicDimensions (AASHTO, 1994), m


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Design Vehicle Type Symbol

Minimum

design

turning radius

(ft)

Minimum

inside radius

(ft)

Passenger car

Single-unit truck

Single-unit bus

Articulated bus

Semitrailer, intermediate

Semitrailer combination, large

Semitrailer-full trailer

combination

Interstate semitrailer

Interstate semitrailerTriple semitrailer

Turnpike double semitrailer

Motor home

Passenger car with travel trailer

Passenger car with boat and

trailer

Motor home and both trailer

P

SU

BUS

A-BUS

WB-40

WB-50

WB-60

WB-62a

WB-67b

WB-96WB-114

MH

P/T

P/B

MH/B

24

42

42

38

40

45

45

45

45

5060

40

24

24

50

13.8

27.8

24.4

14.0

18.9

19.2

22.2

9.1

00

20.717.0

26.0

2.0

6.5

35.0

MINIMUM TURNING RADII OF DESIGN VEHICLES (@ less than 15 kph)

Minimum Design RadiusTurning Radius -The diameter of the smallest circle in which a vehicle cancomplete a U-turn. Turning radius depends on the wheelbase of the vehicle(longer vehicles usually need more space to turn around), and maximum steering

angularity.


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AASHTO Turning Templates


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Static Characteristics

4.0 m

12 m

6.5 m 1.5 m

2.5 m

Truck

Rmin = 12 m(US =12.8m)


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Static Characteristics

2.2 m16.5 m

9.0 m 1.3 m

2.5 m

4.0m

Semi- trailer

Rmin = 12m

(US=12.2m)


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Types of Flow Uninterrupted flow

Disruptions only from other traffic in stream Interrupted flow

Disruptions from external sources (control devices, other traffic streams)

Traffic Flow ParametersMacroscopic traffic flow parameterscharacterize traffic stream as a whole

Traffic volume

Speed

Density

Microscopic traffic flow parameterscharacterize behavior of individual vehiclesin the traffic stream with respect to each other Headway

Spacing


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Traffic Volume defined as the number of vehicles that pass a point on ahighway, or a given lane or direction of a highway, during a specified timeinterval

Unit: vehicles per unit time (ex. vehicles/hour or veh/hr or vph)Common interval: day

Daily volume parametersUnit: vehicles per day or veh/day or vpdDaily volumes are not differentiated by direction or lane but are totals for the

entire facility at a specified location

Annual average daily traffic AADT) = average 24-hr traffic volume at a givenlocation over a full 365-day yearAADT = (total number of vehicles passing the site in a year)/365


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Average annual weekday traffic AAWT) = average 24-hr traffic volumeoccurring on weekdays over a full yearAAWT = (total weekday traffic volume)/260

Average daily traffic ADT) = average 24-hr traffic volume at a given locationfor some period of time less than a year

= ADT may be measured for 6 months, a season, a month, a week or as

little as 2 days

Average weekday traffic AWT) = average 24-hr traffic volume occurring onweekdays for some period of time less than 1 year, such as for a month or aseason

if AADT > AAWT and ADT > AWT, this indicates weekend traffic is heavy andfacility serves primarily for recreational traffic

- daily volumes are useful in highway planning, however, they cannot beused alone for design or operational analysis purposes

- volume varies throughout the day


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Peak-hoursingle hour of the day that has the highest hourly volumePeak-hour volume Directional volume flow directions are separated

Used as basis of highway design and many types of operational analysis

Highways must be designed to adequately serve the peak-hour traffic volume inthe peak direction of flow (both directions of the road facility)

Operational analysis imposition of control measures, safety, capacity Peak-hourly volumes are estimated from daily volume projections

DDHV = AADT K D

where DDHV = directional design hour volume (vph)

AADT = average annual daily traffic (vpd)

K = proportion of daily traffic occurring during the peak

hour, expressed as a decimalD = proportion of peak-hour traffic traveling in the peak

direction, expressed as a decimal

Hourly Volumes


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Short-term peaks of flow within the peak hour may exceed the capacity

Observed volumes are expressed as equivalent hourly rates of flow

ex. 1000 vehicles observed in 15 minutes

= 1000 vehicles/0.25 hr = 4,000 veh/hr

US Highway Capacity Manual suggested a minimum interval for traffic analysis = 15minutes

For 15-minute periods of flow (0.25 =< PHF


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-Rate of motion, in distance per unit time

-Inverse of the time taken by a vehicle to traverse a given distance

S = d 3.6 / twhere S = speed (km/h)

D= distance traversed (m)T= time to traverse distance d (sec.)In a moving traffic stream, each vehicle travels at a different speed

Therefore, a traffic stream has a distribution of individual vehiclespeeds

A typical or average speed may characterize the traffic stream


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-Travel time= total time to traverse a given highway segment;includes stopped delays

-Running time= total time during which the vehicle is in motion while

traversing a given highway segment- does not include stopped delays

-Average Travel Speed= distance of a given segment of roaddivided by average travel time on the given segment

-Average Running Speed = distance of a given segment of roaddivided by average running on the given segment


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Operating Speed = maximum safe speed at which a vehicle canbe conducted in a given traffic stream, w/o exceeding theroads design speed

Difficult to measure; it requires a test car driven through the trafficstream consistent with the definition

Since maximum speed is judgmental matter, consistentmeasurements among test car drivers are not often achieved


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Percentile Speed =speed below which the stated percent of vehicles inthe traffic stream travel

85th percentile speed= often used as the maximum speed limits

15th percentile speed= may be used as a minimum speed for the traffic

stream

50th Percentile speed= median speed = midpoint of speed distribution

Spot speed studies= to determine speeds that drivers select when notaffected by traffic congestion, studies are conducted under conditions

of free flow (light traffic)

Example: if 60 kph is the 85th-percentile speed = 85% of the vehicles in thetraffic stream travel at or below 60 kph


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04 ce 122 traffic characteristics

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