June 30, 2008
Safer Drunk Driving?
A few days ago I wrote a post about one of the uncomfortable truths about drunk driving: As with most things, the more times you do it, the better you get.
The psychology professor who explained this to me said that a lot of the impairment of mild drunkenness comes not from drunkenness per se, but from the unfamiliarity of performing certain tasks while drunk. The first few times you tried to drive a car, you weren't very good at it. Well, the first few times you try to drive drunk, you won't be very good at that either. But in both cases, you get better with practice.
I wasn't mentioning this for any other reason than that I found it interesting. It's an unexpected conclusion that arises from the simple and uncontroversial observation that we get better at tasks when we become familiar with them through practice.
When I thought about it later, it occurred to me that drunkenness is a bit like a disability, and as with any disability, we find ways to work around it. If your knee is injured, you learn to walk a different way so it hurts less. If you're deaf, you learn to talk a different way---sign language and lip reading. So what about drunk drivers? How do they learn to accommodate their self-inflicted disability?
Probably the most obvious accommodation is that they drive slower than normal. This just makes sense: If your reaction time and judgment are screwed up, you slow down so that things happen at a pace you can handle.
Now this has policy implications.
Police are trained to look for driving behaviors that may indicate a drunk driver, and driving really slow is one of them. However, if drunk drivers are aware that police will be more likely to arrest them if they drive slowly, it creates an incentive to drive as fast as everyone else. And faster driving is less safe, especially for a drunk.
To put it another way, when police hunt for drunk drivers, it creates an incentive for drunk drivers to disguise their drunkenness in a way that increases the risk of an accident. This got me wondering if there are other mixed-incentives created by the rules for DUI stops.
(I tried to find the rules for my state, but the Google search just brought up page after page of DUI lawyer sites. One of them probably had the answer, but wasn't about to read all those sites to find it.)
I checked the National Highway Transportation System Administration's DWI Detection Guide. (I'm assuming NHTSA's findings inform state laws and court rulings.) Most of the signs of drunk driving seem like alcohol-induced impairments. Not a problem.
A few of them, however, sound more like they're part of the driver's attempt to reduce the risk of being drunk: stopping too short, slow speed, and slow response to traffic signals.
It's probably safe to assume that if police stop drivers who exhibit these behaviors, it will encourage people to behave differently. Drunk drivers will stop later than they want to, speed up, and take off quickly when the light turns green. All of which may cause more accidents.
None of this proves that these traffic stops are actually increasing the danger. After all, arresting drunk drivers discourages drunk driving, which reduces the danger. At this point we'd have to look at the statistical evidence to figure out which effect is dominant. That's more work than I feel like doing for a blog post.
My gut feeling (if it's good enough for Steven Colbert, it's good enough for me) is that the increase in danger is small compared to the advantages of arresting drunk drivers, so we shouldn't stop using behavior like slow driving as a cue to stop someone.
Maybe we can split the difference, however. We could reduce the penalties for drunk driving if it's done more safely. You'd flip that around for enforcement purposes, by specifying an enhanced penalty if the car's speed was more than 10 mph below the limit.
I suspect a similar set of incentives applies to drunk drivers who pull off the road to sober up. Police have actually found drunk people pulled over and asleep behind wheel and arrested them for DUI because they were legally still considered to be in control of the car. Is it really a good idea to discourage drunk drivers from getting off the road to sober up?
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