Identifying the Impact of Truck -Lane Restriction Strategies on Traffic Flow and Safety Using Simulation

The continuous growth of freight transportation over recent years has resulted in an increasing proportion of commercial vehicles on our nations’ highways, which has led to higher truck volumes and more severe truck-related crashes every year. Safety proponents have therefore been advocating for more restrictions to be placed on these commercial vehicles in order to reduce the interaction of these larger vehicles and passenger cars. A popular strategy is the use of different lane restrictions for trucks. However, the effectiveness of these restrictions for trucks differs from case to case due to unique factors of each site, including the type of restriction used, traffic conditions and the geometric characteristics at the site. This has motivated the author to conduct this study to evaluate the impact of these restrictions on traffic operations and safety on freeways with different traffic and geometric characteristics. For the safety evaluation, this research measures the impact of different truck lane restriction strategies (TLRS) using conflict as the measurement of effectiveness (MOE). Conflict has been proven to be highly related to traffic crushes on freeways (FHWA, 1990; Sayed and Zein, 1999; Kaub, 2000). The high frequency of conflicts has also made it possible to collect adequate data for statistical analysis. The MOEs used to evaluate the impact of different lane restrictions on operational performance were lane changes, average speed, speed distribution, and volume distribution. Due to the lack of existing highway locations with different lane restrictions considered in this study, the conflict data were collected using a traffic simulation tool – PARAMICS V3.0 (Quadstone Ltd., 2000), which can simulate the emergent interaction between vehicles but not random crashes on the road network. The effectiveness of different lane restrictions in terms of the above MOEs were evaluated for 14,400 different simulation scenarios by varying lane restriction strategies, traffic conditions (volume, truck percentage) and geometric characteristics (gradient, speed limit, interchange density). The simulation results showed that all the geometric and traffic characteristics had a significant impact on freeway safety and operation. In addition, truck percentage and volume were identified as key factors that had a significant impact on the selection of the optimal truck lane restriction strategy. The ANOVA analyses indicated that the degree of effect of truck lane restriction strategies on safety intensify with the increase in truck percentage and traffic volume. Optimal alternatives of truck lane restriction strategies under different truck percentages and volumes were identified with the objective of reducing traffic conflicts and enhancing LOS (level of service). Guidelines were then developed for the application of truck lane restrictions under alternative traffic and geometric conditions.

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