Accident Models for Two-Lane Rural Segments and Intersections

Data collected from the states of Minnesota and Washington on rural two-lane highways are used to build accident models for segments and three-legged and four-legged intersections stop-controlled on the minor legs. The quantity, quality, and variety of data collected, together with the advanced techniques applied in the analysis, make this study of special interest. Variables include traffic, horizontal and vertical alignments, lane and shoulder widths, roadside hazard rating, channelization, and number of driveways. Models are of negative binomial and extended negative binomial form and yield R 2 values from 0.42 to 0.73 and overdispersion parameters from 0.20 to 0.51. A segment model combining both states and including state as a variable, and intersection models derived from Minnesota data, are featured, along with summary statistics, goodness-of-fit measures, and cross-validation between the states. Segment accidents depend significantly on most of the roadway variables collected, while intersection accidents depend primarily on traffic. The study recommends development of adjustment factors for different regions and times and further development of extended negative binomial models.