Ignition interlocks are devices that can be installed in vehicles to prevent operation by a driver who has a blood alcohol concentration (BAC) above a specified level. Interlocks are most often installed in vehicles of people who have been convicted of alcohol-impaired driving. Interlocks can be mandated by courts or offered by state licensing agencies as an alternative to a suspended driver’s license, often as a provision of a restricted license. Requirements for use of interlock devices varies by state based on BAC level, number of offenses, and other conditions. Interlocks are generally installed for the length of time a license would be suspended, usually 6 to 24 months (CG-Motor vehicle injury). States can levy penalties on offenders for failure to install devices (CDC-Ignition interlock).

• Reduced impaired driving

• Reduced alcohol-related crashes

There is strong evidence that installing ignition interlock devices for people convicted of alcohol-impaired driving reduces re-arrest rates while interlocks are installed (CG-Motor vehicle injury, Miller 2015c*). When removed, however, re-arrest rates are similar to those convicted of alcohol-impaired driving who do not use interlocks (CG-Motor vehicle injury, Miller 2015c*, IAS-Anderson 2006). Ignition interlock devices have also been shown to reduce alcohol-related crashes (McGinty 2017*, Ullman 2016, McCartt 2013*).

Drivers with interlocks appear to have fewer alcohol-related crashes than drivers whose licenses have been suspended for an alcohol-impaired driving conviction (CG-Motor vehicle injury, IAS-Anderson 2006). States with laws that require interlock use for all drunk driving offenders, including first-time offenders, have greater reductions in crash rates and crash-related deaths than states with laws that require interlock use for high-risk offenders (e.g., repeat offenders) only (McGinty 2017*, Kaufman 2016*, Ullman 2016). A Washington-based study also indicates that interlock installation requirements for first-time offenders decreases recidivism and crashes (McCartt 2013*).

As of 2017, every state has an ignition interlock law, although specifics vary. Twenty-nine states and Washington DC have mandatory ignition interlock provisions for all convicted drunk driving offenders. Florida, Hawaii, New Jersey, North Carolina, Wisconsin, and Wyoming require ignition interlocks for first-time convicted offenders with a certain BAC level or higher (MADD-Ignition interlock 2017).