Rural Expressway Intersection Characteristics as Factors in Reducing Safety Performance

Abstract

Expressways have been constructed in many states as a way to increase mobility without the expense of a full access-controlled grade-separated facility. In most cases, it was assumed that these segments of highway would produce similar mobility and safety characteristics as other access-controlled facilities. However, recent research has found that there are problems with the safety performance of these systems. The objective of these analyses is to identify the major contributing factors that create problematic intersections in Iowa. From previous research, it is evident that factors in addition to roadway volume contribute to the safety performance of an at-grade, two-way, stop-controlled expressway intersection. This research identifies additional characteristics that may increase or decrease the safety performance of a rural expressway intersection. The methodology used in this research includes the examination of 644 intersections throughout Iowa. Through the use of a statewide database and crash information from 1996 to 2000, it was possible to identify, on the basis of crash severity rate, the 100 best-performing and 100 worst-performing expressway intersections. With these 200 intersections, a statistical analysis was completed to determine the effects intersection design and surrounding land use have on an intersection's safety performance. Skewed intersections, intersections located on vertical or horizontal curves, and intersections at which there is varying surrounding land use were studied to determine their effects on safety performance. Following the completion of the analysis of the 200 intersections, the 30 intersections with the highest crash severity index rates were selected for more thorough, site-specific analysis. As part of this analysis, the authors examined the impact of land use adjacent to the intersection and of peaking in hourly traffic volumes. The research identifies attributes that impact crash frequency and severity both negatively and positively.