Do ignition interlocks stop drunk driving?

Allie Johnson

Drivers who get behind the wheel drunk and get caught - such as Reese Witherspoon's husband Jim Toth, who in April 2013 was arrested for DUI in a highly publicized incident in Atlanta - might be forced to prove they're sober before they can hit the road again.

Many states now require convicted drunk drivers to get ignition interlock devices on their vehicles in order to keep their driver's license. In fact, 33 states now require ignition interlocks for first-time offenders caught driving with a certain blood alcohol level, according to Mothers Against Drunk Driving (MADD). The device typically must stay on the car about six months for a first-time offender or about a year for a repeat offender, Harris says.

ignition interlockIn 17 states, including New York and Virginia, that level is .08, while in other states, such as Alabama and Wyoming, it's .15 or, in a few states, higher. And in eight states, including Ohio and Pennsylvania, ignition interlocks are mandatory only after a second drunk driving conviction.

In some states, a convicted drunk driver who does not want to use the device might have other options, says Steven Oberman, a Tennessee attorney certified as a DUI defense specialist. For example, in Tennessee, drivers can sometimes get a license that has restrictions on where and when they can drive. They might be able to drive to and from work, church and substance abuse treatment - but not to a doctor appointment or the grocery store, he says.

How do ignition interlocks work?

So, how exactly do ignition interlocks work? Here are the steps:

1. You go to a designated service station to have an ignition interlock installed. States usually offer a list of approved interlock manufacturers, and those companies display a map or list of approved installers on their websites. An ignition interlock consists of a hand-held breathalyzer-type device that is connected to the car's ignition.

2. When you get in your car, you blow into a mouthpiece on the handheld device. If sensors detect alcohol on your breath above a low pre-programmed level, the car won't start for a set time period - usually about five minutes, says Frank Harris, state legislative affairs manager for MADD. This gives you time to figure out whether the high reading could have been caused by something like mouthwash and, if so, to rinse your mouth and try again.

3. The devices come equipped with ways to prevent drivers from circumventing the technology. Some ignition interlocks contain a camera that snaps a photo of your face as you blow into the mouthpiece, Oberman says. Those images are stored in the device, along with other data. The photos can later be checked to verify that it was the driver who blew into the interlock device every time. And some interlocks require you to hum or suck after you blow into them, Harris says, which prevents drivers from getting around the test by deflating a balloon into the mouthpiece.

4. If you test below the set alcohol threshold - often about .02, Oberman says - you will be able to turn the key, start your car and begin driving. As you drive, the interlock will periodically alert you that you must blow into it again within a certain amount of time, usually about five minutes.

That gives you time to pull over or wait until you're stopped at a red light. These measures ensure that the driver is the person who initially blew into the device. "This way you can't just have your friend blow into it for you in the bar parking lot before you start driving," Harris says.

5. Once every month or two - or sooner if you try to drive after you've been drinking - you will take your car back to the service station that installed the interlock. A technician will check the device and upload all of the data it has recorded, such as blood alcohol levels, times and dates the vehicle was started and stopped, and photos of the person who blew into the interlock. The data is sent to government officials in charge of monitoring the driver. For example, in Arizona, records are sent to the state motor vehicle division.

Do ignition interlocks stop drunk driving?

Ignition interlocks are a cost-effective way to keep offenders from drinking and driving and to keep the public safe, Harris says, likening them to a "virtual probation officer".

The devices can be used in conjunction with DUI schools and treatment for alcohol abuse. And, he says, interlocks are more effective than some other measures, such as a long driver's license suspension with no monitoring.

A 2012 study in Washington state by the Insurance Institute for Highway Safety (IIHS) showed that first-time DUI offenders who used ignition interlocks were less likely to be arrested again in the next two years for alcohol-impaired driving than those who didn't use the device. "They do work," Kristin Nevels, spokeswoman for the IIHS, says of ignition interlocks.

The devices are not cheap, and it's often the offender who pays for them, experts say, though some low-income offenders can get a device for free. Getting an ignition interlock installed on your car typically costs $100 to $250, and there's usually a monthly lease fee of $65 to $90 - or about the cost of one drink a day, according to the National Highway Traffic Safety Administration.

But Oberman says some of his clients pay as much as $200 per month. And that's not the only financial cost of a DUI: the insurance consequences can be severe. In some cases, the insurance company will move you to a higher-risk category and raise your premiums, or they might refuse to renew your policy, says Carole Walker, executive director of the Rocky Mountain Insurance Information Association. Your rates could double or even quadruple, she says.

Another drawback: ignition interlocks are not foolproof, Oberman says. For example, some drivers get false positive readings that show alcohol on their breath after they eat certain foods, including bread. And one of his clients, a perfume saleswoman, got several false positive readings in a row when the device detected alcohol from the perfume she kept in her car, Oberman says.

But overall, ignition interlocks are beneficial: "Anything that makes the roads safer is a positive thing," Nevels says.