Traffic and Highway Engineering
5th Edition
ISBN: 9781305156241
Author: Garber, Nicholas J.
Publisher: Cengage Learning
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Question
Chapter 9, Problem 1P
To determine
The traffic characteristics with each of the levels of service for primary freeway sections.
Expert Solution & Answer
Explanation of Solution
Introduction:
Level of service is a qualitative method which is used to describe the operating conditions of a given freeway segment. This method uses density as the variable and alphabetic grading system raging between A to F.
There is 6 basic level of service, which is described below.
- Level of service A.
- Level of service B.
- Level of service C.
- Level of service D.
- Level of service E.
- Level of service F There is a complete blockage in the traffic flow.
The vehicles move freely within the traffic stream without any interruption. Effect of incidents or point breakdown is easily absorbed.
Traffic moves under reasonably free flow condition with minimum restrictions. Effect of incidents or point breakdown is easily absorbed.
The speed of the vehicles is almost equal to free flow speed, but the free flow of the vehicles is constrained. The driver has to be cautious while shifting lanes. Small incidents are absorbed but large incidents direct to queuing of vehicles.
In the traffic stream, the free movement of vehicles is very much restricted, and there is no level of comfort. Even a minor incident leads to queuing of vehicles.
There are no good gaps between the vehicles, and the operations are unbalanced. The entry of vehicles from ramps or sub-lane leads to a blockage in the traffic flow.
Conclusion:
There are six levels of service which are represented alphabetically from A to F. Level of service A being the ideal for driving with decreasing free flow and level of service F being congested.
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Briefly describe the traffic characteristics associated with each of the levels of service for basic freeway sections.
Describe the factors that affect the level of service of a freeway section and the impact each has on flow.
A long segment of suburban freeway is to be designed on level terrain. The level segment, however, is followed by a 4.5% grade, 2.0 miles in length. If the DDHV is 2,500 vehicles per hour with 15% trucks (standard mix), how many lanes will be needed on the (A.) Upgrade, (B.) Downgrade, (C.) Level terrain segment to provide for level of service C? Lane widths and lateral clearances may be assumed to be 12 feet and 6 feet, respectively. Ramp density is expected to be 1.0 ramps per mile. The PHF is 0.92. Good weather, no incidents, no work zones, and regular users of the facility may be assumed.
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Traffic and Highway Engineering
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