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Ignition Interlocks
A Proven Means for Preventing Impaired Driving Re-Arrests

Mug of Beer and Keys

A man decides it's best to not have a drink in a restaurant with friends. He has to drive home, and since his arrest for driving while intoxicated (DWI) a few months ago, he's had a court-ordered ignition interlock installed in his car. This device prevents the car from starting if there's alcohol on his breath. A woman puts her children in their booster seats, blows into an ignition interlock, and starts her car's engine. Since her conviction for DWI, she hasn't been faced with the dilemma of how to get her kids to school and drive to work. The court mandated she have an ignition interlock installed rather than have her license suspended. She's thankful that she can drive legally, as long as her interlock detects she's not impaired by alcohol.

Ignition interlocks can be installed in DWI offenders' vehicles as safeguards to help prevent impaired driving—a serious public health problem that kills about 11,000 people and costs nearly $110 billion annually.

When someone is convicted of DWI and arrested, it's clear that they've made the decision, at least once, to drink and drive. It's important to take steps to prevent them from making such a risky decision in the future. Devices known as ignition interlocks can be installed in DWI offenders' vehicles as safeguards to help prevent future episodes of impaired driving—a serious public health problem that kills about 11,000 people annually and costs nearly $110 billion a year.

When an ignition interlock is installed in a car or truck, it prevents that vehicle from being driven by anyone with a blood alcohol concentration (BAC) above a specified level. This level is usually 0.02 to 0.04 grams per deciliter (g/dL); the minimum illegal BAC level is 0.08 g/dL in every state. Typically, interlocks are installed in vehicles operated by drivers who have already been convicted of DWI. They may be mandated through the court system or offered as an alternative to a suspended license, and they're usually installed for 6 to 24 months.

Interlocks can be effective in both preventing DWI offenders from driving while intoxicated and for reducing their re-arrest rates for DWI. The Centers for Disease Control and Prevention's (CDC) Community Guide Branch conducted a systematic review of 15 scientific studies on ignition interlocks. Researchers found that while these devices were installed, re-arrest rates for alcohol-impaired driving decreased by a median of 67 percent relative to comparison groups.

Unfortunately, only a small proportion of DWI offenders currently participate in interlock programs. As of December 2010, only 13 states require interlocks for all convicted offenders, including a first conviction. More than half of all states require some offenders—such as those with multiple convictions or an extremely high BAC at the time of arrest—to install ignition interlocks.

Interlocks can be effective in reducing re-arrest rates and in preventing those already at risk for impaired driving from operating their vehicles if they've been drinking. Because of the evidence of their effectiveness, the Community Preventive Services Task Force recommends more widespread use of interlocks by people convicted of DWI. CDC recommends ignition interlocks for everyone convicted of DWI, even for first convictions. Impaired driving can be prevented, and ignition interlocks are an important and effective step to reducing the problem.

CDC's Injury Center works to protect the safety of everyone on the road, every day. For more information about impaired driving and motor vehicle safety, please visit www.cdc.gov/motorvehiclesafety. For more information about the results of the review of studies on ignition interlocks, including full-text articles released in the March 2011 issue of the American Journal of Preventive Medicine, see www.thecommunityguide.org/mvoi/AID/ignitioninterlocks.html.

The Community Guide

The Community Guide is an essential resource for people who want to know what works in public health. It provides evidence-based recommendations and findings about public health interventions and policies to improve health and promote safety. The Community Preventive Services Task Force -- an independent, nonfederal, volunteer body of public health and prevention experts -- makes these findings and recommendations based on systematic reviews of scientific literature conducted under the auspices of the Community Guide. CDC staff provides ongoing scientific, administrative and technical support for the Task Force.

Scientific Methods

The Community Guide conducts state-of-the-art systematic reviews that: analyze all available scientific evidence on what works to promote health and prevent disease, injury and disability; assess the economic benefits of the interventions found to be effective; and identify critical evidence gaps. Community Guide review teams are led or supported by Community Guide scientists, and include government, academic, policy and practice-based partners.

Visit Reducing Alcohol-Impaired Driving for information about additional recommended strategies. You can learn more about other Community Guide systematic reviews, including reviews specific to Preventing Excessive Alcohol Consumption by visiting Community Guide topics.