Alcohol ignition interlocks are a proven way to reduce repeat offenses for driving while intoxicated (DWI), but given a choice most offenders don't voluntarily put them in their vehicles. Even when installation is mandatory, some offenders may sidestep the requirement by agreeing not to drive at all or claiming not to have a vehicle. When the alternative is house arrest, though, convicted DWI offenders pick interlocks 7 out of 10 times. This is the main finding of a Pacific Institute for Research and Evaluation study of one New Mexico county's experience with interlocks.
The study looks at Santa Fe, where four judges agreed to a 2-year pilot to sentence all DWI offenders, including first-timers, to home confinement via electronic monitoring as an alternative to interlocks if they claimed to have no car or no intention to drive. The aim was to boost DWI offenders' use of interlocks.
At the time, the state required interlocks for all convicted multiple DWI offenders and first aggravated offenders (BACs of 0.16 percent or higher).
Interlocks prevent alcohol-impaired drivers from starting their vehicles. Drivers blow into a breath-testing unit and must register a blood alcohol reading below a preset level, which is usually well under the legal blood alcohol concentration (BAC) threshold of 0.08 percent, in order to start the vehicle. If the reading exceeds the level, the engine won't turn over.
Researchers compared Santa Fe's installation rates between June 1, 2003, and May 31, 2005, with all other New Mexico counties. During this period, 70 percent of drivers convicted of DWI in Santa Fe installed interlocks, compared with 17 percent in other counties. The finding is in line with a 2002 study of a similar program in Hancock County, Indiana.
The judges stopped using the house-arrest option in 2006 after a state court rejected this sanction. Santa Fe's interlock installation rate fell 19 percentage points in the 2 years following the program's termination. But installations rose in most other counties during the 2006-07 period after New Mexico began to require interlocks for all convicted DWI offenders, not just those committing an aggravated offense.
New Mexico's results show that "motivating interlock installation by providing a less desirable alternative to the interlock can substantially increase the number of DWI offenders who install interlocks," the authors note.
Interlocks successfully reduce the risk that repeat offenders will commit further violations, a 1999 Institute study found. Interlock restrictions reduced the risk of committing an alcohol-related traffic violation within the first year following conviction by nearly 65 percent (see "Ignition interlocks reduce re-arrest rates of alcohol offenders," Jan. 15, 2000).
More than half of all U.S. states require DWI/DUI offenders to install ignition interlocks on their vehicles in order to drive during a license suspension and/or require interlocks for specified time periods before fully relicensing offenders.
In New Mexico and 12 other states, all offenders must get interlocks to legally drive during the suspension period. California applies a similar restriction to all offenders but only in 4 counties. Nine more states apply the restriction to all offenders with high BACs (usually 0.15 percent or higher) and to repeat offenders, and 6 states apply the restriction to only repeat offenders. Courts or motor vehicle departments in 18 states and the District of Columbia have the discretion to require interlocks.
Vermont and Minnesota in May adopted interlock laws, both of which take effect in July 2011. Vermont will allow DWI offenders, including first-timers, to shorten license suspension by installing an interlock. Vermont had been among the 3 states, along with Alabama and South Dakota, with no interlock laws. Minnesota's law covers high-BAC and repeat offenders.
Last month Tennessee amended its existing interlock law to authorize courts to require interlocks for high BAC offenders as part of a restricted driver's license, in addition to repeat offenders covered under the prior law. The revised law allows first offenders to voluntarily ask to drive only an interlock-equipped vehicle at their own expense, even if the court doesn't order them to use one. The law takes effect in January 2011.