The rate of fatal car accidents is highest in the fall, with October being the most dangerous month. On average, October sees 10.2 deaths per billion kilometers traveled, according to the study that was recently published in the journal Traffic Injury Prevention.
Using data on distance traveled and road fatality rates from the Department of Transportation, Michael Sivak of the university’s Transport Research Institute calculated the fatality rate per distance driven for every month from 1994 to 2006. He found that October, November and December have the highest rates with the lowest rates coming in March at 8.8 deaths per billion kilometers.
“The risk of a fatality per distance driven in October is about 16% greater than the risk in March,” Sivak said. “Everything else being equal, inclement weather — snow and ice — should increase the risk of driving. However, because inclement weather also leads to general reductions in speed, the net effect is not clear.”
Sivak also said that several factors more prevalent during the summer suggest that the fatality risk should be higher during those months.
“For example, leisure driving, which occurs more frequently on unfamiliar roads, at higher speeds, at night and under the influence of alcohol, is riskier than commuter driving,” he said. “Although hard data are not available, leisure driving is likely to be most frequent during summer months when school is out. In addition, consumption of beer shows a strong seasonal variation, peaking in summer months.”
So what is it about driving in the fall and early winter that is so dangerous? The most likely factor is the increase in the duration of nightly darkness, but Sivak says there is no single cause to blame.
“There are several known factors with major influences on the risk of driving that show strong seasonal variations,” he said. “However, the peaks and troughs of the seasonal variations of these factors do not fully match the pattern of the overall driving risk. Thus, the driving-risk pattern is likely a consequence of joint contributions of several factors.”
Photo courtesy of Charlie Anzman under the Creative Commons License.