Analysis of Highway Design and Geometric Effects on Crashes

Project summary:

Forty percent of fatal highway crashes in Minnesota are road-departure crashes. Road geometry (e.g. curves or tangential sections) and road design (e.g. lane width, shoulder width, shoulder pavement type) likely play a role in these crashes. Previous research indicates that two key elements of design (horizontal curvature and shoulders) are primary factors affecting crash frequency and severity. However, the actual effect on crash frequency is not well documented; most of the cited safety strategies are considered experimental or tried (as opposed to proven), so that effectiveness ratios are questionable, and none of the supporting data are from Minnesota. This study addressed these shortcomings with three key objectives: 1) identify the features or characteristics associated with shoulders (type and width) and curve geometry (degree of curve and frequency) that affect road-departure crashes, 2) determine where design changes or countermeasures have been deployed, and whether these practices or other countermeasures have quantifiably decreased the frequency and/or severity of these crashes, and 3) identify which emerging technologies could be used as appropriate countermeasure(s) to reduce the frequency and/or severity of these crashes. The final report reviews both infrastructure and emerging in-vehicle solutions as a means to determine the optimal deployment strategy of countermeasures designed to improve highway safety. Infrastructure-based solutions are examined on two levels: 1) an analysis of a cross-section of strategies implemented throughout Minnesota, which 2) produced a before:after analysis that quantified the effectiveness of a variety of strategies utilized in Minnesota.