Does Separating Trucks from Other Traffic Improve Overall Safety?

Decision-makers have long speculated that building separate roads for trucks and passenger cars, or at least separating them on their own lanes would accomplish two major objectives: 1) they would make the roadways safer for passenger cars, and 2) roadways designed specifically for a select class of vehicles rather than for all vehicles might represent overall savings in construction costs. This paper addressed the first objective. Recent studies on the evaluation of safety effects of truck traffic levels on general freeway facilities have not provided a clear understanding on how they affect the number of crashes. In some cases, they have been contradictory. In addition, no studies have specifically compared passenger cars-only with mixed traffic freeway facilities. The original research on which this paper is based is aimed to assess whether or not more homogeneous flows of traffic by vehicle type are safer than the current mixed flow scenario. To accomplish the objective of the study, an exploratory analysis of crash data is conducted on a selected number of freeway sections located on the New Jersey Turnpike for the year 2002. These sections operate as a dual-dual freeway facility: divided inner and outer lanes. At these locations, the inner lanes have the special characteristic of being for passenger cars only (homogeneous traffic). The selected sections, therefore, offer a very good opportunity to compare the crash experience between passenger car-only and mixed traffic rural freeway facilities. The results of the study show that outer lanes experience more crashes, both when raw numbers are used and exposure is included into the analysis. It shows that truck-related crashes contribute significantly to the total number of crashes on the outer lanes. In fact, trucks are overinvolved in crashes given the exposure on these sections. Even though the outcome of this study suggests that separating truck traffic from passenger cars for freeway facilities improves safety, further work is needed to understand the contributing factors leading to truck-related crashes in the outer lanes.