The Breathalyzer Behind the Wheel

Here are two compelling facts about ignition-interlock devices for preventing drunk driving. One is that these devices are highly effective, despite the logical possibilities for bypassing them. The second is that they are rarely installed in the cars of people who have been known to drive while intoxicated.

People driving while intoxicated still cause about 13,000 deaths a year in the United States. And of the 1.4 million arrests made, one-third involve repeat offenders. The greatest potential of ignition interlocks is to reduce this recidivism.

These hand-held devices, typically attached to dashboards and connected to the ignition, use fuel-cell technology to measure the concentration of alcohol in a person’s breath. Although they are made by various companies, all ignition interlocks conform to strict standards of accuracy set by the National Highway Traffic Safety Administration. If too much alcohol is detected, the car will not start.

A person who has been drinking might naturally think of fooling the device by persuading a sober person to start the engine, but that is not enough to subvert the system, because the device requires breath samples while the person drives — at random intervals of five minutes to an hour. (At least one company is also integrating cameras with the interlocks to photograph the driver when he provides a breath sample.) The unit keeps a log of all tests, and it is sealed so that any attempts at tampering can be detected.

Ignition-interlock devices are not perfectly effective; a drunk can often borrow another car. But in one recent study they were found to reduce repeat drunk-driving offenses by 65 percent. If they were widely installed, the devices would save up to 750 lives a year, a recent National Highway Transportation Safety Administration report estimated.

Many states have recognized their potential. Eight states now mandate that interlocks be installed in the cars of all drunk-driving offenders, and another 25 require them for repeat offenders or those whose blood-alcohol content was far higher than the legal limit. Still other states give judges the option to order interlock installation. But implementation of these measures has lagged.

Judges often fail to order installation, even when the law requires it. Offenders routinely ignore orders to get interlocks. And in areas where the installation is voluntary, few offenders install them. In 2007, only about 146,000 interlocks were in use.

Part of the problem is that many already overburdened courts may lack the resources to monitor compliance. Some states make driver’s license renewal conditional on the installation of an ignition interlock, but there is often inadequate integration between courts and motor-vehicle departments. Finally, the cost of the interlocks discourages people from complying with court orders.

The price of renting and maintaining a unit is $70 to $100 a month, and installation can be another $70 to $175. These charges increase the offender’s temptation to simply drive without a license.

How can we get more drunk-driving offenders to use interlocks? Better oversight by, and coordination among, authorities would help, as would efforts to make the units less expensive. New Mexico, which has been a leader in interlock legislation, has created a special fund to help pay the cost for low-income people. This has the side benefit of helping judges overcome their reluctance to order the use of interlocks.

It is also important to link ignition interlocks to substance-abuse treatment. Currently, court orders simply specify that the units be installed for a fixed period of six months to two years, regardless of whether the person has shown progress in curbing his drinking problem. That helps explain why, as research has shown, the devices have no lasting effect on the likelihood that a person will be arrested for drunk driving again after the interlock order is lifted. Mandates for interlocks should be tied to requirements for substance-abuse treatment, and removal of the devices should not be allowed until the offender has gone for an extended period without trying to start his car after drinking. The ignition interlock could be an extraordinarily effective way to prevent drunk-driving recidivism. But it can save lives only if we make sure people use it.

Philip J. Cook, a professor of public policy at The Sanford School of Public Policy Duke University, is the author of “Paying the Tab.” Maeve E. Gearing is a doctoral candidate in public policy at Duke. This commentary was first published in The New York Times on Aug. 30, 2009