At face value, the Insurance Institute for Highway Safety's newest report should be filed under obvious: making it harder for convicted drunk drivers to drive while intoxicated decreases the number of people who drive under the influence more than once. As the report would suggest, however, an intricate justice system is at hand in the fight to reduce drunk-driving deaths.
At hand is a fairly simple device called an ignition interlock, a device that forces a driver to breathalyze him/herself before starting the car. If the interlock finds that a driver's blood alcohol content, or BAC, is above the legal limit of 0.08, it will not let the driver start the car.
The IIHS's report, "Washington State's Alcohol Ignition Interlock Law: Effects on Recidivism Among First-time DUI Offenders" focuses on the state of Washington as it changed its laws dealing with convicted drunk drivers. In 1999, Washington legislators passed a law which allowed judges to force drivers who either refused a breathalyzer during their traffic stop, was convicted multiple times of driving under the influence of alcohol, or blew a 0.15 or above to drive with an interlock for one year. Five years later, they changed the policy to include first-time offenders and those who blew between 0.08 and 0.15.
Looking at the results, it's fairly obvious that ignition interlocks are effective. The study showed that about three percent of people who were convicted of DUI for the first time between July 2004 and June 2006, and installed an interlock, were convicted again during the two years after their arrest. For those who didn't install the interlock despite government orders to do so, that recidivism rate is roughly 13 percent.
The main point here by the IIHS isn't, then, that interlocks work--that's already been determined. What the report said was that Washington's expansion of the law was effective. And it was: the report showed that the two-year recidivism rate among first-time offenders in the second quarter of 2006 was 9.3 percent, 1.3 points below where the IIHS estimates it would have been without the expansion.
The situation gets a bit more complicated because not every driver who is convicted of a DUI eventually gets an interlock: interlock among convicted drunk drivers went from around five percent before the expansion to about a third afterwards. IIHS researchers predicted that if every convicted drunk driver used an interlock, the recidivism rate would be something like half of what it is today.
What's standing in the way of that? During the study period, interlock use wasn't compulsory: around 30-40 percent of DUI drivers plea-bargained their way into convictions for offenses like reckless driving, which doesn't come with an interlock, and drivers who were assigned interlocks could opt for license suspensions during the interlock period (generally one year). That second loophole was largely closed in 2011: convicted drivers who want to regain their licenses need to post at least four months of interlocked driving to regain their licenses.
Intricacies of the legal system aside, the IIHS says that the bottom line is that deterrents work: make it harder for people to drive drunk more than once, and they'll do it with less and less frequency. The next steps: working with surrounding states to replicate this system. Considering that drunk driving deaths fell precipitously in the 1980's and 1990's but have stagnated in the years since, the IIHS seems to be chasing many avenues to reduce deaths once again.
Source: Insurance Institute for Highway Safety