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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.
TRB's Commercial Truck and Bus Safety Synthesis Program (CTBSSP) Synthesis 3: Highway/Heavy Vehicle Interaction reports on the safety interactions of commercial trucks and buses with highway features and on highway improvements that can be made to improve the safety of heavy vehicle operations.
In recent years, increases in truck traffic on Virginia's highways have raised issues concerning safety and capacity on interstates such as I-81 and I-95. Lane restrictions represent a strategy that is intended to reduce conflicts between trucks and cars and facilitate traffic flow. Field experiments to determine the effects on existing traffic under lane restrictions for an interstate freeway segment are usually not feasible, and an alternative approach was selected. In this study, the simulation model FRESIM was used to estimate various traffic flow elements. The purpose of this study was to analyze changes in traffic flow elements (density, lane changes per vehicle, and speed differential) under conditions of restricted and unrestricted truck lane configurations. Prior to application of the simulation model to actual sites in Virginia, a scenario analysis was completed. The scenario analysis tested the variability of each traffic flow element considering the following variables: traffic volume, percentage of trucks, percentage of total volume by lane, presence or absence of lane restrictions, and grade. A statistical paired-sample t test was used to determine significant differences in the values of the three traffic flow elements when lane restrictions were applied. An analysis was also completed for three case studies in Virginia, located on I-81 near Buchanan, Christiansburg, and Wytheville. Two types of restrictions were tested: restricting trucks from the left lane and restricting trucks from the right lane. From the results obtained in this study several conclusions were drawn: (1) restricting trucks from the left lane with steep grades causes an increase in speed differential and may decrease density and the number of lane changes, (2) restricting trucks from the right lane causes an increase in the number of lane changes, and (3) site characteristics dictate the effects of truck lane restrictions. Based on the results of this study, it is recommended that (1) trucks be restricted from the left lane when grades are 4 percent or greater and (2) trucks not be restricted from the right lane. The study results did not support removal of truck lane restrictions in Virginia.
With the increased expansion of rural Interstates to six lanes, questions have arisen as to the proper operational strategy of those facilities. One approach is to restrict trucks and other large vehicles from one or more of the lanes. The effects of such a restriction, however, have not been extensively studied. This study analyzes the operational effects of three left-lane truck restrictions on six-lane rural Interstates in Texas. Although the directional distribution of trucks changed significantly, no effects were found on the directional distribution of cars, the time gaps between vehicles, or the speeds of either cars or trucks that could be attributed to the truck restriction.
Increases in heavy truck traffic on Virginia's highways in recent years have raised concerns about both safety and capacity, particularly on the interstate system. Transportation agencies have developed a number of strategies for dealing with the impacts on safety and capacity of a truck population that has been increasing in volume and in the percentage of large tractor-trailers. One strategy that has been suggested is separate lanes for trucks and passenger vehicles. A reliable methodology to determine when separate lanes for trucks and passenger vehicles are economically feasible would enable transportation officials to make informed decisions concerning when this approach should be considered and used. This study evaluated a computer program, Exclusive Vehicles Facilities (EVFS), developed by the Federal Highway Administration for determining the economic feasibility of separating trucks and other vehicles on freeway segments. A 50.7-km (31.5-mi) segment of 1-81 in Virginia was selected to demonstrate the application of the program. A number of factors contribute to the feasibility of exclusive lanes. Although no single factor predominates, traffic volume, vehicle mix percentage, accident rates, and maintenance and construction costs are given more weight than other factors in the program. Among the program's strengths are its ability to analyze a number of alternatives for a variety of different conditions, its ease of use, and the fact that it can be inexpensively applied. Its weaknesses include its inability to differentiate between the lane(s) (i.e., inside, middle, outside) to which restrictions are applied and its unsuitability for analyzing exclusive lane alternatives in which a barrier is used to separate vehicle types. With respect to 1-81, several exclusive lane strategies produced a benefit-cost ratio greater than 1.0 and a net present worth in the millions of dollars. Should 1-81 or another high-volume interstate corridor with a large truck percentage be considered for improvement, VDOT should apply EVFS to assist in evaluating the feasibility of exclusive lane alternatives. Since EVFS is designed to perform economic analyses, operational and geometric implications of any exclusive lane strategy should also be considered.
Achieving sustainable transport requires more than 'optimal' management of congestion and the effects on public health and the environment. This book is organized into three sections, each discussing a major set of challenges to the transition to a sustainable transport system.