Researchers who studied thousands of traffic accidents over a 20-year period came up with a finding that even they found surprising: Female drivers are far more likely to run into a car driven by another woman than a man.
The study is bound to add fuel to the debate over whether men are better drivers than women, but the researchers insist that was not their intent, and the study falls short of supporting that conclusion.
Michael Sivak of the University of Michigan's Transportation Research Institute, who is lead author of the study published in the Traffic Injury Prevention journal, said in a telephone interview that he and his colleague, Brandon Schoettle, wanted to determine if there is a gender interaction component in traffic accidents. They did indeed find it, he said, but they didn't expect the difference between men and women drivers to be nearly as great as the research indicates.
He called the difference "astounding."
The researchers examined police reports of two-vehicle traffic accidents across the country from 1988 to 2007 and they zeroed in on the cases in which the drivers of both vehicles could "potentially" determine the gender of the other driver in the moments before the crash. The accidents occurred during "personal travel" and since men drive about 60 percent of the time compared to 40 percent by women, the researchers assumed men would be involved in more accidents than women.
The "expected" percentage of accidents in which both drivers were men should be around 36 percent, but the chances that a woman would run into another woman was expected to be less than 16 percent, because women drive less than men.
Those expectations turned out to be so far out of whack that the researchers themselves could hardly believe it.
Women 'Overrepresented' in Accidents
Crashes involving two female drivers were "overrepresented" in five out of six different crash scenarios: Variations on crossing another vehicle's path, side-swiping, turning in front of another vehicle, and head on. But here's the baffling part - when both vehicles were driven by a female, the crashes exceeded the expected frequency by at least 50 percent in two scenarios, and more than 25 percent in three others.
The percentage of accidents in which a woman sideswipes another female driver to her left came in at a whopping 52 percent compared to the expected frequency of 15.8 percent. In the same type of accident involving two male drivers, the percentage was 22 percent below the expected level of 36.2 percent.
Similarly, if a female crossed the path of an approaching vehicle driven by another woman, the number of accidents was 50 percent above the expected level of 17 percent.
The percentage of accidents involving one male and one female driver were close to the expected level for all six scenarios.
In a nutshell, what that says is a woman is far more likely to crash into another woman than a man, but a man is less likely than expected to crash into another man.
What the research doesn't explain is why that should be the case. Sivak said in a telephone interview that the study clearly shows there is a gender interaction component in traffic accidents, but he doesn't know why female drivers are so "overrepresented" in accidents involving two women. The study begs for clarification, but he said it may not be possible to answer the question of why.
At least one other study debunked the idea that men are better drivers than women are. Researchers at Johns Hopkins University found that female drivers were involved in slightly more crashes then men, but the difference was not all that great -- 5.1 crashes per million miles driven for men, compared to 5.7 crashes for women.
Age, in various studies, appears to be a more important issue than gender. Teenage boys start off badly, according to the Johns Hopkins study, with about 20 percent more crashes per mile driven than teen-age girls. Between the ages of 20 and 35 males and females are equally at risk of being involved in a crash, and after age 35 female drivers are at greater risk than males.
Other research has found that many factors, including gender, contribute to traffic accidents, especially those resulting in injuries. A Purdue University study found, for example, older men and women are much more likely to die from traffic injuries than younger persons, regardless of gender.
And according to another study just released by Sivak and Schoettle, just driving in a state other than the one in which you live can be deadly. They looked at fatal accidents in all 50 states and found a huge difference in the number of fatal accidents involving an out-of-state driver.
"There is a wide variability across the 50 states in the percentage of all drivers involved in fatal crashes who were out-of-state drivers, with a minimum of 5.0 percent in California to a maximum of 41.2 percent in Wyoming," that study concludes.
Why? Perhaps the vast plains of Wyoming lend themselves to higher speeds than the jammed freeways of California.