Safety Impacts at Intersections on Curved Segments

Abstract

Indiana geometric design policy, consistent with national standards, allows for the design of intersections on superelevated curves if other solutions are prohibitively expensive. Consequently, the Indiana Department of Transportation (DOT) has built a number of such intersections. Following a series of fatal crashes at one of these intersections, Indiana DOT made a decision to avoid designing intersections on segments with steep superelevation. This design restriction calls for expensive alternatives, such as realigning roads or adding grade separations. This research was done to determine whether superelevated intersections were more hazardous than similar intersections located on tangents and, if so, to determine what combination of factors made this true. The research focused on two-way stop-controlled intersections where the mainline was a high-speed four-lane divided highway located on a superelevated curve. An attempt was made to analyze as many factors as possible by using appropriate comparison techniques. Negative binomial models were developed to determine the statistical relationship between crash occurrence and intersection geometric characteristics, including curvature of the main road. Crash severity and the joint impact of curvature with weather and lighting conditions were examined by using binomial comparisons of proportions. Research findings show significant increases in crash frequency and severity at intersections located on superelevated curves.