OPERATIONAL PERFORMANCE MODELS FOR FREEWAY TRUCK-LANE RESTRICTIONS

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OPERATIONAL PERFORMANCE MODELS FOR FREEWAY TRUCK-LANE RESTRICTIONS











Summary of Final Report, BD015-01
April 2003



OPERATIONAL PERFORMANCE MODELS FOR FREEWAY
TRUCK-LANE RESTRICTIONS


PROBLEM STATEMENT
Highways are designed to facilitate the flow of various modes of traffic, including passenger cars, trucks, buses, and recreational vehicles. The fact that the impacts of these different vehicle types are not uniform, however, creates problems relating to highway operations and safety. Passenger car volume has increased over the last decade, as have truck operations, both in terms of volume and dimension. Consequently, highway planners must address a number of distinct issues in order to enhance the safety of our highways. A common approach to reducing the impacts of truck traffic on freeways has been to restrict trucks to certain lane(s) to minimize the interaction between trucks and other vehicles and to compensate for their differences in operational characteristics. Many possible design alternatives for truck-lane restrictions exist. Some use one restricted lane while others use two or more; some restrict trucks to the rightmost lane(s) while others restrict them to the leftmost lane(s). The performance of these different truck-lane restriction alternatives differs under different traffic and geometric conditions. Thus, an effective estimate of the operational performance of different truck-lane restriction alternatives under prevailing conditions is needed to help make informed decisions regarding truck-lane restriction alternatives.
OBJECTIVES
The objective of this project is to develop operational performance models that can be applied to help identify the most operationally efficient truck-lane restriction alternative on a freeway under prevailing conditions. The operational performance measures examined include average speed, throughput, speed differentials, and lane changes. Prevailing conditions include number of lanes, interchange density, free-flow speeds, volumes, truck percentages, and ramp volumes. The developed performance models will provide the information needed to determine such issues as the levels of truck and non-truck volumes needed to justify the implementation of a specific truck-lane restriction alternative and the expected travel speeds and throughput for a corridor before and after the implementation of a truck restriction method.
FINDINGS AND CONCLUSIONS


The analysis of simulated data resulted in the following findings and conclusions:
1. In general, truck restriction alternatives increase the average speed under conditions of low
interchange density, low truck volume, and low ramp volume. When a freeway corridor is congested with densely spaced interchanges, high truck percentages, or high ramp volumes, truck-lane restrictions reduce the average speed. However, the speed reduction is negligible,









except when a large number of restricted lanes is used (