Who Drives Better, Men or Women?

We’ve established that men are more likely to take the wheel when a couple rides together, but should we care? I say we should. Aside from the cultural, sociological and psychological implications, the gender driving disparity might be costing us lives and treasure. If women are more skilled drivers than men, perhaps we’d all be better off if they were behind the wheel and men were in the passenger seat knitting. What do the data say?
Despite comprising half the population, women drivers are unquestionably involved in many fewer accidents than men are. In fact, it isn’t even close. Insurers are well-aware of this fact (see this from the Australian insurance company AAMI), and hence they often charge women lower premiums.
So there it is: women have fewer accidents than men. Time to move the driver’s seat up?
Not quite-we haven’t yet heard the whole story (and we all know that once that seat is moved? you can never again get it as comfortable as you once had it).
The problem is that if we’re trying to determine whether men or women should take the wheel when the couple is in the car, aggregate accident totals are of limited usefulness.
Why? Because men drive lots more than women do. The American Time Use Survey shows that adult men average about 60 minutes a day behind the wheel, while women average around 40. The National Household Transportation Survey reports that in 2001 men averaged 16,749 miles driven per year, and women 10,174. Given that they drive so much less, it’s not particularly surprising that women are involved in fewer accidents and pay lower premiums.
To really answer our question we need to look at data adjusted for “exposure,” that is, the amount of time people spend behind the wheel. In our case, what we’re looking for is accidents per mile driven.
Research (gated) by Guohua Li, Susan P. Baker, Jean A. Langlois and Gabor D. Kelen showed that, as of the mid-1990s, women drivers were involved in about 5.7 accidents per million miles driven. Men, on the other hand, were involved in about 5.1. Women were thus 12 percent more likely to be in crashes per mile driven. This is confirmed by another paper (gated), by Dawn L. Massie, Kenneth L. Campbell, and Allan F. Williams, which found women were involved in 16 percent more accidents than men on a per mile driven basis.
We might want to think not just about accidents, but about the severity of those accidents. Here again, it doesn’t look good for the ladies. Massie et al. found that for each mile driven women were 26 percent more likely than men to be in crashes involving injuries.
So there we have it; with men having fewer accidents and fewer injury accidents per mile, all those women driver jokes from my grandparents’ generation can be dusted off and put to good use.
Or can they be?
If we move to the next level of severity, fatal accidents, we find quite a different picture. Li et al. found that male drivers are 80 percent more likely to be in a fatal accident than women on a per mile basis. Massie et al. confirmed this, finding men are 55 percent more likely to be in fatal crashes. More recent data,?collected by the Insurance Institute for Highway Safety, paints an almost identical picture.
Thus women are somewhat more likely to be in crashes, but men are lots more likely to be in very severe crashes. According to AAMI:

Men are more likely than women to be involved in serious accidents – that is, men experience more head-on collisions, roll-overs, loss-of-control crashes and collisions involving pedestrians, cyclists or animals whereas women are more likely than men to collide with stationary objects or reverse into other cars.

So if saving lives is our goal, perhaps it’s time the women take the wheel, and we allocate transportation stimulus funds to a team of comics to craft an all-new set of male driver jokes to be used by future generations.
Well, maybe. Even given these data, a number of factors might be clouding the picture. For one thing, I don’t have data on who was at fault in accidents (one study had this but didn’t do per mile exposure). I suppose it’s possible that one sex or the other has a greater propensity to be the innocent victim in accidents, but it strikes me as unlikely.
Another complicating factor could be the driving environment. For example, Jeff Wise, author of Extreme Fear: The Science of your Mind in Danger, has blogged in this space about the fact that freeways are considerably safer than surface roads. If men do a higher share of their driving on the freeways (and I suspect that this is the case due to differing commuting patterns), this would make them appear to be less dangerous drivers than they really are. Also, it’s possible that since men do most of couples’ driving they are more likely to be behind the wheel at night when visibility is poor.
In this vein, another possibility is that the tradition of the man driving is keeping the truly terrible female drivers off the road, and thus our population of women drivers exhibits selection bias. In that case, handing women who don’t currently drive the keys might have exactly the opposite of the intended effect.
In any event, to truly understand this issue we need to dig a bit deeper to find not just the numbers, but the reasons for what’s going on. More on this coming up.