Rural Expressway Intersection Characteristics that Contribute to Reduced Safety Performance

Abstract

Expressways have been constructed in many states as a way to increase mobility without the expense of a full access-controlled or grade-separated facility. In most cases, it was assumed that these segments of highway would produce mobility and safety characteristics similar to other access-controlled facilities. However, recent research has found that there are problems with the safety performance of these systems associated with conventional at-grade, median-opening intersections. Although past research has been completed to examine the nature of crashes on these facilities, it is the purpose of this study to continue the research and analyze the common characteristics of the intersections. The intersections studied in this research were located throughout the state of Iowa. The objective of these analyses is to identify the major contributing factors that create problematic intersections in the state of 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 common 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 the state of Iowa. Through the use of a statewide database and crash information from 1996 to 2000, we were able to identify the 100 best and 100 worst performing intersections based on crash severity rate. For the 200 intersections, a statistical analysis was completed to determine the effects of intersection design and location has on safety performance. The safety performance of vertical/horizontal curve location, intersection skew, and land use were studied to determine the effects on rural expressway intersections. Following the completion of the analysis of the 200 intersections, 30 intersections with the highest crash severity index rates were selected for more thorough site-specific analysis. As part of this analysis, we examined the impact of land use adjacent to the intersection and the impact of peaking in hourly traffic volumes. The research identifies attributes that impact crash severity both negatively and positively. Through the identification of these attributes, designers and planners can more adequately address safety concerns on rural expressway intersections.