Road Weather Management Program
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Best Practices for Road Weather Management Version 2.0


Effects of Adverse Weather on Traffic Crashes: Systematic Review and Meta-Analysis


It is reasonable to assume that adverse weather will impact vehicle crash rates on roads and highways. However, it would be very valuable to quantify the extent to which weather conditions impact the crash rate. To address this need, meta-analysis has been conducted to generalize research findings on this subject and attempt to quantify the impact of weather on traffic crashes. Studies between 1967 and 2005 that examined the interaction of weather and traffic safety were reviewed. Thirty-four papers and seventy-eight records that meet the predetermined criteria were included in the analysis. The crash rates from each study were normalized with respect to effect size or percent change for meta-analysis generalization. The results indicate that crash rate usually increases during precipitation. Snow has a greater effect than rain on crash occurrence: Snow can increase the crash rate by 84 percent (95 percent confidence interval [CI] =0.68, 0.99), injury rate by 75 percent (95 percent CI = 0.54, 0.96). Further results also suggest variations in studies results can be explained by study design, date of the study, and the region or countries included in the study.


87th Transportation Research Board (TRB) Annual Meeting, University of Iowa. For an electronic copy of this resource, please direct your request to

Date: 2007


Qiu, Nixon



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