Abstract

This paper examines the impacts of truck lane restriction on urban freeways using traffic simulation models. The study includes three main parts: Part (1) provides insights into conditions under which truck lane restrictions would work well; Part (2) identifies the best number of lanes to restrict and shows that this is an important factor in the success of lane restriction; Part (3) investigates potential impacts of truck lane restriction through a case study using a region with some of the highest truck volumes in the U.S., the I-710 corridor in Los Angeles County, California. The study begins by examining the potential impacts of truck lane restrictions using two representative hypothetical freeways. This is because the impacts of truck lane restrictions will vary with differing traffic and geometric conditions. Results suggest that truck lane restriction could work well when the rate of flow is more than 1300 vehicles per hour per lane and where trucks make up at least 10 percent of the total traffic. Three scenarios are developed. These are do-nothing (no strategy implemented), alternative I (the one leftmost lane restricted from trucks), and alternative II (the two leftmost lanes restricted from trucks). These are examined in a pair-wise manner. Results show that determining the best number of restricted lanes is very important. Through the I-710 case study we find that alternative II would have the most positive effects on traffic congestion and travel time variance. Based on these results, we conclude that truck lane restriction strategies, which are very simple and cost-effective to implement, may contribute to improved traffic flow on urban freeways.

Abstract

Trucks are a major contributor to non-recurrent congestion in the region that comprises Los Angeles, Ventura, and Orange Counties of California. In 1987, for example, a total of 5,203 mainline freeway collisions (i.e., no ramp or connector collisions) involving trucks were reported (according to the state-maintained records of California Highway Patrol field investigations) in this tri-county region. Approximately 91 percent of all mainline truck incidents on Southern California freeways occur on weekdays (Monday through Friday) and 95 percent of these weekday freeway incidents occur during the period of heavy freeway usage (6:00 a.m.–6:00 p.m.) with approximately 56 percent occurring during the morning (6:00 a.m.– 9:00 a.m.) and evening (3:00 p.m.– 7:00 p.m.) peak periods. This amounts to an average of approximately 19 truck incidents per weekday on the tri-county freeway system, the majority of which (15 per day) occur on the heavily traveled freeways of Los Angeles County. 

With congestion increasing on this and other metropolitan freeway systems, it is important to determine the impact of truck-related incidents on the freeway system, and to seek ways to mitigate this impact. The research reported here focuses on a particular aspect of the truck incident problem: Estimation of the impact of truck-involved collisions on the operation of the freeway system in terms of total delay. (Non-collision incidents, such as stalls and spilled loads, are not included in this analysis.)

Abstract

To better understand how road congestion adversely affects trucking operations, we surveyed approximately 1200 managers of all types of trucking companies operating in California. More than 80% of these managers consider traffic congestion on freeways and surface streets to be either a “somewhat serious” or “critically serious” problem for their business. A structural equations model (SEM) is estimated on these data to determine how five aspects of the congestion problem differ across sectors of the trucking industry. The five aspects were slow average speeds, unreliable travel times, increased driver frustration and morale, higher fuel and maintenance costs, and higher costs of accidents and insurance. The model also simultaneously estimates how these five aspects combine to predict the perceived overall magnitude of the problem. Overall, congestion is perceived to be a more serious problem by managers of trucking companies engaged in intermodal operations, particularly private and for-hire trucking companies serving airports and private companies serving rail terminals. Companies specializing in refrigerated transport also perceive congestion to be a more serious overall problem, as do private companies engaged in LTL operations. The most problematic aspect of congestion is unreliable travel times, followed by driver frustration and morale, then by slow average speeds. Unreliable travel times are a significantly more serious problem for intermodal air operations. Driver frustration and morale attributable to congestion is perceived to be more of a problem by managers of long-haul carriers and tanker operations. Slow average speeds are also more of a concern for airport and refrigerated operations.