Reconsidering the Impact of Access Spacing on Crash Risk

About the report:

The spacing of access points is one of the most critical elements in access management. This project aims to investigate the effect of access spacing on crash risk using scientifically rigorous statistical methods and to examine VDOT’s current access spacing standards. Specifically, the study focuses on unsignalized access types located on principal arterials, minor arterials, and collectors.

A comprehensive literature review was conducted, examining the directionality and magnitude of the safety impacts of access spacing, the selection of exposure indicators, and the statistical methods employed. An experiment was designed to compare the crash outcomes of 33 control sites with large access spacing and 33 experimental sites with short access spacing. Random effects negative binomial (RENB) models were developed and identified as the appropriate approach to explore the safety impact of access spacing while accounting for exposure indicators and other factors such as the number of turn lanes and sight obstructions.

Results indicated that shorter spacing significantly increased total crashes but had no significant effect on severe crashes. Moreover, it was found that violating VDOT’s minimum access spacing standards would increase total crashes by 64.8%. Based on these findings, the study recommends that VDOT should continue to maintain its current minimum spacing standards for accesses. Adhering to these standards can help prevent escalating crash costs in the long term.

Supplemental material may be found at: https://library.vdot.virginia.gov/vtrc/supplements

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