The purpose of this study was to investigate the number of motor vehicle crashes, injuries, and deaths that occurred in the United States in years 2010 — 2014 in relation to the weather conditions and weather-related roadway surface conditions present at the time of the crash. The data examined were a representative sample of all police reported crashes and a census of all fatal crashes that occur on public roads in the United States. The average number of injuries and fatalities per 1,000 crashes was computed as a measure of the severity of crashes that occur under various weather and surface conditions. Poisson regression was used to adjust crash-based rates of injuries and fatalities for other factors associated with crash severity. Nationwide, an average of 1,179,253 police-reported crashes, 425,103 injuries, and 5,137 deaths occurred in adverse weather and/or roadway surface conditions annually, representing 21.0% of all crashes, 18.5% of all injuries, and 15.6% of all fatalities during the study period. Crashes that occurred in adverse weather or on slippery roads were more likely to be single-vehicle crashes than crashes that occurred in clear weather and on dry roads. A larger proportion of all crash-involvements of younger drivers than of older drivers occurred in adverse weather and/or roadway surface conditions. Crashes that occurred in adverse weather and/or roadway surface conditions were less likely to result in injuries or fatalities than crashes on dry that occurred in clear weather and on dry roads. After adjustment for other factors related to crash severity, crashes that occurred on snow-covered roads resulted in 31% fewer injuries per crash and 47% fewer fatalities per crash than crashes that occurred on dry roads; crashes that occurred on icecovered roads resulted in 19% fewer injuries per crash and 29% fewer fatalities per crash than crashes that occurred on dry roads. The only weather condition associated with a statistically elevated rate of fatalities per crash was fog–crashes that occurred in fog resulted in 155% more fatalities per crash than crashes that occurred in clear weather after adjustment for other factors associated with crash severity. An important limitation of this study is that it did not investigate effect of adverse conditions on the risk of crashes occurring; only the number and severity of crashes could be investigated due to limitations of available data. The finding that crashes that occur in adverse conditions tend to be less severe than crashes that occur in clear weather and on dry roads may be attributable to drivers driving more slowly and carefully in bad weather and on slippery roads, however, it is also possible that adverse conditions increase the risk of crashes of all severities but disproportionately increase the risk less severe crashes. Other studies suggest that precipitation is generally associated with increased crash rates, and that the increase in lower-severity crashes is larger than the increase in higherseverity crashes. Given the large number and proportion of crashes, injuries, and deaths that occur in adverse weather conditions, more effort is needed to educate motorists regarding safe driving practices in inclement weather and to develop and implement vehicle technologies to improve the safety of driving in inclement weather. (Author/publisher)
Abstract