Comparisons of Crashes on Rural Two-Lane and Four-Lane Highways in Texas

The selection of the cross section for a roadway is a critical decision in the design process. This decision substantially impacts safety, capacity, and cost. Although capacity and cost considerations are generally readily evaluated, the impact of the cross section on safety is not always apparent. Lane width and shoulder width can have a significant impact on safety of rural two-lane and four-lane highways. Prediction models were used to generate estimates of the percent change in crashes between different shoulder or lane width decisions. These values can be used when evaluating alternatives. The prediction equations can also be used to identify the mean crash value over roadway segments of similar conditions. An upgrade for a rural two-lane highway to a rural four-lane divided highway with full shoulders can provide significant crash reductions. A conversion from a two-lane with wide shoulder cross section to a four-lane with narrow shoulder cross section should be considered only at very high average daily traffic counts and wide surface widths based on safety. Several variables were found through the literature and through this research that affect crash prediction at rural intersections. Those elements that can be influenced by designers with the greatest benefits in decreasing crashes include left-turn lanes, lighting, and wider right shoulders.