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Is Driving Drunk Rational?

I doubt this statement will shock you or light up the blogosphere, but drunk driving is bad. Our own Levitt has looked at the costs, and found that those who have had even one drink are seven times more likely to cause a fatal crash, while for those over the legal BAC limit the risk is multiplied by 13. This equates to a cost to society of more than 40 cents per drunk mile driven (2013 dollars), implying that a fine of $10,500 would be appropriate if drunk drivers were to bear the full cost of their actions.

The good news is that we have made tremendous progress. According to the National Highway Traffic Safety Administration, road fatalities due to drunk driving have dropped from 21,113 in 1982 to 9,878 in 2011. The decrease is even more remarkable given that total miles driven almost doubled during that period. So the drunk driving fatality rate per billion miles traveled has dropped from 13.4 to 3.4 in the last 30 years.

Some of this is due to general improvements in driving safety, such airbags and increased seatbelt use. But this is only a part of the equation. A suite of policies specific to alcohol has also been implemented, with considerable success. These have been recently analyzed by Susan A. Ferguson and Koyin Chang, Chin-Chih Wu, and Yung-Hsiang Ying, among others. Successful policies have included toughening laws and their enforcement, such as reducing permissible blood alcohol content (BAC) levels, especially for underage drinkers. Sobriety checkpoints are a very effective enforcement mechanism, particularly if properly publicized. Other policies that have been found to be effective are higher alcohol taxes (very), and to a lesser extent laws banning open alcohol containers in cars and higher legal drinking ages.

What about tougher penalties? It seems pretty obvious that these must work, but the evidence is surprisingly mixed. “Zero tolerance” for drunk drivers below 21 seems to be effective, and license suspension has shown some results, although the story here is somewhat equivocal. (For example, many of those who have lost their license continue to drive, illegally, albeit less frequently and more carefully. One strategy for dealing this might be impounding the offender’s vehicle). Breath alcohol ignition locks are also very effective—but only when in use: The evidence shows offenders tend to return to their old habits when they are removed. The brief incarceration that often follows a DWI stop has not been shown to be much of a deterrent.

This goes to the larger debate about the link between severity of punishment and criminal recidivism, which is not as cut and dried as you might think. In fact, some studies actually show harsher prison conditions increase recidivism upon release. For example, it is possible that prison is a “crime school” and that more time behind bars hanging around with other criminals may make one more likely to learn new tricks. Other work shows severe punishments do work, but it is not crystal clear why. Because punishment persuades people crime doesn’t pay? Or because incarceration keeps criminals off the street?

The theory that harsher punishment causes people to alter their calculus about the profitability of crime is in line with the assumptions of classical economics, which hold that man is a perfectly rational computer, with complete information, who calculates the potential value of future actions and chooses the path with the highest expected returns. In the case of crime, economist Gary Becker pioneered the theory that a potential criminal should multiply his chances of getting caught by the potential costs of the penalty (presumably with time spent behind bars converted to a monetary value) and weigh this against the benefits he gets from lawbreaking. However, we all know that in reality we’re rarely smart enough to do this.

The flaws in the rational man conceit are why behavioral economics is such a hot topic in the field; economists have moved beyond thinking about the way that people should behave to the way they do behave. How do tough penalties affect us psychologically?

Benjamin Hansen, an economist at the University of Oregon whose work I’ve written about in the past, recently presented a conference paper that looks at this question in the case of drunk driving. Specifically, he examines whether people commit fewer crimes because of fear of what may happen to them if they do (“deterrence”) versus what they’ve learned emotionally from punishments that have already happened to them (called “specific deterrence”).

Hansen’s study takes advantage of a large database of DUI offenders in Washington State, which has laws similar to the rest of the US. The key to the study is that there are two definitions of DUI: the regular old garden variety offence if BAC is over .08, and “aggravated” DUI with a level over .15. Aggravated DUI brings a harsher punishment for the offense in question, but it has no special effect on the level of punishment for the next offense (which rises in severity the same amount no matter the level of the prior conviction).

First, Hansen finds that having been convicted and punished for a DUI reduces the chances of getting caught with a DUI in the future. Since the punishment scale for DUI ramps up with prior convictions, this appears to fit with the standard theory that harsher punishment is a deterrent for reoffending.

However, one aspect of Hansen’s findings call the model of the rational criminal into question. Since there is no extra future penalty for those convicted of an aggravated DUI, if drunk drivers rationally calculated the future cost of punishment they would all have the same odds of reoffending regardless of the level of their past conviction. However, Hansen finds that those who got aggravated DUIs were actually less likely to reoffend, all else equal. This suggests that the experience of having received harsh punishment teaches you a lesson. This is called a “learning effect.” Another implication is that drunk drivers may not fully understand the system of punishment, and base their estimation of the cost of the next conviction on past experience and not accurate knowledge of the law.

These findings are interesting in terms of both psychology and deterring crime. They suggest that increased sanctions for drunk driving—such as lower permissible BAC levels, longer license suspensions, ignition lock systems, and harsher fines—are indeed likely to have additional deterrent effects. In fact, Hansen computes that raising penalties by 10 percent would reduce drunk driving by about 4 to 7 percent, and this is just counting the effects on repeat offenders and not deterrence for those who have never been caught. However, there is one catch; the positive impacts of such a learning effect would take a while to play out, as the deterrent will only mount as people get caught and punished over time.

As for psychology, it probably doesn’t come as a surprise that criminals suffer from “bounded rationality,” and with possible rare exception of a Bernie Madoff or a Unabomber probably lack the mathematical acumen to calculate the present and expected future value of their crimes. I’d be quite interested to know if, given that the extra penalty from an aggravated DUI is a “sunk cost” which according to economic theory any rational person should disregard,  chronically drunken economists are more likely to reoffend than the rest of us.