Rural expressway intersection characteristics that contribute to a reduced safety performance

Burchett, Garrett
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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 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. 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 provide an identification of 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. With the 200 intersections, a statistical analysis was completed to determine the effects intersection design and surrounding land use have on the intersection's safety performance. The safety performance of intersections located on vertical/horizontal curves, skewed intersections, and varying surrounding land use were studied to determine their effects on rural expressway intersections. Following the completion of the analysis of the 200 intersections, 30 intersections with 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.