Sep 23, 2016

Effects of Rainfall on Vehicle Crashes in Six U.S. States

Alan Black, Gabriele Villarini, and Thomas Mote
American Meteorological Society
  • Explores crash risk during rainfall for six US states (Arkansas, Georgia, Illinois, Maryland, Minnesota, and Ohio) using daily gridded precipitation and county level crash data
  • Examines risk from the perspective of daily total rainfall, citing previous US studies that found a positive relationship between risk and daily accumulation
  • Results provide a comprehensive assessment and quantification of the role played by rainfall in increasing car crashes, injuries and fatalities over broad areas of the eastern and central United States
  • Key findings include:
    • Overall crash risk increased by 26% on days with rainfall totals greater than or equal to 12.5 mm as compared to days without rainfall; by 32% on days with 25 mm of rainfall or more; and by 51% on days with 50 mm or more
    • Overall injury crash risk saw similar increases of 20%, 26%, and 38% over dry days when receiving daily rainfall ≥ 12.5 mm, ≥ 25 mm, and ≥ 50 mm, respectively
    • Relative risk is significantly higher in urban counties as compared to rural interstate or rural counties
    • Relative risk is about 5% higher in urban counties than in rural interstate or rural counties when examining all rainfall related crashes, but is 20% higher than rural interstate and 30% greater than rural counties for days with at least 50 mm of rainfall
    • For injuries, the relative risk in urban areas is 5% higher than rural interstate or rural areas when considering all crashes, but increases to 16% and 29% respectively on days with at least 50 mm of rainfall
    • While rural counties have a 26% increase in crash risk on days with rainfall ≥ 50 mm, the crash risk in urban counties is 55% higher, more than double the risk in rural areas and a significant finding given the large number of motorists in urban counties
  • States that these are important findings with respect to climate change, because increases in the frequency and/or intensity of rainfall under changing climate would be expected to result in more crashes