A $100 Device Prevents 67% of Repeat Drunk Driving. 80% of Offenders Never Install It.

According to the toxicology reports, we solved repeat drunk driving in the 1990s. An ignition interlock is a breathalyzer wired to your starter motor. Blow over the limit, the car stays parked. MADD counted 3.78 million blocked start attempts over 14 years of deployment.^[1] The IIHS ran the numbers across every state from 1999 to 2016 and found all-offender interlock mandates reduce drivers with BAC at or above 0.08 in fatal crashes by 26 percent.^[2]

That 26 percent figure describes what happens when the device is on the dashboard. The GAO investigated what happens in the real world and found that somewhere between 15 and 20 percent of convicted DUI offenders actually install the thing.^[3] The rest drive without a license, plead down to reckless driving, or simply ignore the court order in states too understaffed to check. Thirty-four states now mandate interlocks for all DUI offenders, including first-timers. Sixteen states still reserve the requirement for repeaters or high-BAC cases only.

Run the arithmetic on 2025 traffic data: NHTSA counted 36,640 fatalities last year, roughly 31 percent of them alcohol-impaired: approximately 11,358 deaths.^[4] If every state had an all-offender law and every offender complied, the IIHS reduction factor erases 2,953 of those deaths. At the actual 15-20 percent compliance rate, the real-world savings shrink to roughly 440-590. That leaves a compliance gap of about 2,400 preventable deaths per year sitting in the space between the statute and the steering wheel.

Washington state provided the natural experiment when the state expanded its interlock mandate to all offenders in 2004, then tightened it twice more by 2011. Recidivism for first offenders fell from an expected 7.7 percent to 5.6 percent, but installation rates never cracked 38 percent.^[2] IIHS researchers estimated that full compliance would have pushed recidivism to 2 percent. Part of the reason it didn't: prosecutors started reducing DUI charges to negligent driving, which carries no interlock requirement. When those plea bargains were excluded from the calculation, the installation rate jumped to 54 percent. The loophole was doing more work than the law.

The economics border on absurd. An interlock runs the offender $70 to $150 per month, or roughly $1,200 to $1,800 per year. DOT values a statistical life at $14.2 million. If universal compliance saved 2,400 lives, the societal return would be roughly $34 billion against a compliance cost of around $2.25 billion (1.5 million annual DUI arrests times $1,500 average annual interlock cost), a 15-to-1 return. You would be hard-pressed to find a public health intervention with better math and worse follow-through.

The GAO found one more discomfiting result: once the interlock is removed, DWI re-arrest rates revert to pre-interlock baselines.^[3] The device is a leash, not a cure. It works while bolted to the dashboard and stops working the day it comes off. The standard objection writes itself: treat the underlying alcohol use disorder instead of strapping a breathalyzer to the steering column. Fair. But only 7.6 percent of people with alcohol use disorder receive any treatment in a given year.^[5] Interlocks are the tourniquet; treatment is the surgery, and we are currently applying neither at scale.

If you have a prior DUI, check your state's interlock laws at your DMV website. If your state does not require interlocks for first offenders, your legislators chose a body count over a $100 device. You should tell them you noticed.