Utilizing an encroachment probability benefit-cost model to estimate accident reduction factors

Abstract

Improving safety on Texas roadways is a major public concern. Over the years, the Texas Department of Transportation and other highway agencies have become interested in reducing society's accident cost while maximizing returns on accident reduction investments. This focus has led to the implementation of a highway safety, cost effectiveness procedure. Two approaches are currently being used by States Department of Transportation. One approach is encroachment probability based, the other is accident data based. The encroachment probability procedure has been heretofore under-utilized by transportation professionals. This research evaluates the ability of a new encroachment probability based procedure to determine accident reduction factors for a set of typical countermeasures. Close attention is paid to the effects on accident costs induced by changes to traffic volume, lateral offset, and type of countermeasure application. The evaluation is achieved via trend data and analysis of changes to input parameters. A comparison of program generated accident reduction factors to the factors currently being used by the Texas Department of Transportation and other states is an extension of the evaluation process. The results indicate a reduction in accidents as lateral offsets from the edge of pavement increased, and an increase in accident costs as traffic volumes increased. The magnitude of reduction factors differed with respect to countermeasure application. Recommendations were made in support of the use and application of this methodology. This procedure can be utilized when deciding what types of safety applications should or should not be used. This methodology is a pro-active tool for decisions on roadside safety; and has the historical records are unavailable. General system-wide safety related guidelines can also be established with a full-scale implementation of this methodology.