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Traffic EngineeringCONTENTS1. Traffic Characteristics2. Intersections3. Pedestrians4. Parking5. Accidents and Traffic safety6. Road Classification7. Traffic Management (or Traffic Control)

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Speed-volume Relationship

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Level of service Flow condition M/C

ratioA Free flow, with low volumes and high speeds. < 0.4

B

The zone of stable flow, with operating speeds beginning to be restricted somewhat by traffic conditions. Drivers still have reasonable freedom to select their speed and lane of operation.

0.4 - 0.6

CLevel of Service C is still in the zone of stable flow, but speeds and maneuverability are more closely controlled by the higher volumes.

0.6 - 0.8

DLevel of Service D approaches unstable flow, with tolerable operating speeds being maintained, though considerably affected by changes in operating conditions.

0.8 - 0.9

ELevel of Service E cannot be described by speed alone, but represents operations at even lower operating speeds than in Level D, with volumes at or near the capacity of the highway.

0.9 - 1.0

FLevel of Service F describes forced flow operation at low speeds, where volumes are below capacity (stop-and-go mechanisms).

> 1.0

Levels Of ServiceTraffic congestion is expressed in terms of Level of Service (LOS). Level of service is a letter from “A” for excellent conditions to “F” for failure conditions.

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Spee

d

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LOS Representation

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Intersections LOS

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Pedestrians LOS

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DefinitionsThe capacity of a road "C" is the maximum number of vehicles that can pass a point (or transfer a section) on a road under a desirable condition in one hour (vehicles per hour).

The occupancy of a road (or actual traffic volume) "M" is the number of vehicles that can pass a point (or transfer a section) on a road in one hour (vehicles per hour).

Road Network Elements

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Traffic densityThe Traffic density "D" expresses the number of vehicles in a given length (usually one km) of a road and measured in vehicles per km.

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Density

Traff

ic

Volu

me

Spee

dTraffic Volume-Density-Speed Relationship

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Diverging

Crossing

Converging

Weaving

Traffic conflicts

Conflict Points

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Traffic Conflict Points (Examples)

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Intersections with priority control (with traffic signs)

Lag acceptance behavior can be studied by observing driver reactions at a priority intersection. It is noted whether the minor road driver accepts the lag and drives out into the major road, or rejects the lag and remains in the minor road. The acceptable lag "tg" is measured in seconds.

Gap and Lag acceptance by minor road drivers

Cumulative Distribution for Accepted and Rejected Gaps

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N

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DelaysThe factors affecting the delays at Intersections with Priority control are: Actual traffic flow on the minor road "Nact" and the acceptable traffic flow on the minor road "N". The total delays "w" is calculated in hours and the average delays "tw" in sec./h/vehicle.

7. The traffic flows at a T-leg junction under priority control are illustrated diagrammatically in the following Figure. The values of the traffic flows are given in vehicles per hour. It is required to calculate the theoretical capacity of the junction, assuming the per cent of right turning flow 55 % and the acceptable lag 6.0 seconds.

Solution

8. The traffic flow at a T-leg junction under priority control is illustrated diagrammatically in the following Figure. The values of the traffic flows are given in vehicles per hour. Define the benefits that can be obtained by widening the major road to be two lanes in each direction (instead of one), assuming that the acceptable lag is 6 seconds and the per cent of right tuning flow is 75 %

Solution

9. The traffic flows at a crossroads under priority control are illustrated diagrammatically in the following Figure with the values of the traffic flows in vehicles per hour. Define the benefits that can be obtained by widening the minor road to be two lanes, assuming that the acceptable lag is 4.0 seconds and the actual lag 1.5 seconds.

Solution