Econometric analysis of the effect of roadway geometric and roadside features on run-off-roadway accident frequencies and severities

In the U.S., single-vehicle run-off-roadway accidents result in a million highway crashes with roadside features every year and account for approximately one third of all highway fatalities. Despite the number and severity of run-off-roadway accidents, quantification of the effect of possible countermeasures has been surprisingly limited due to the absence of data (particularly data on roadside features) needed to rigorously analyze factors affecting the frequency and severity of run-off-roadway accidents.; This study provides some initial insight into this important problem by combining a number of databases, including a detailed database on roadside features, to analyze runoff-roadway accidents on a 96.6-kilometer section of highway in Washington State.; To quantify the effects of roadside features on accident frequency and severity, statistical models are estimated. For accident frequency analysis, negative binomial and zero-inflated negative binomial models of monthly accident frequency were estimated, and accident severity were studied with a nested logit model. The findings isolate a wide range of factors that significantly influence the frequency and severity of run-off-roadway accidents. The marginal effects of these factors are computed to provide an indication on the effectiveness on potential countermeasures. The findings show promise for the methodological approach undertaken and provide important directions for future research.