Do ignition interlock devices actually cause more accidents?

If you’re convicted of drunk driving in Tennessee or 33 other states, you could be required to have an ignition interlock device installed on your car. This device is kind of like a breathalyzer. It is hard-wired into your car’s engine — at your expense — and requires you to provide a clean breath sample before the engine will start.

There is some concern that a particularly stubborn driver might just bring their alcohol along for the ride and get drunk on the road. The ignition interlock has a plan for that eventuality. It randomly requires the driver to provide a clean breath sample while they are actually driving. If the driver fails to do so, the headlights begin flashing and the horn begins honking until the engine is turned off.

Unfortunately, as the New York Times recently reported, providing a rolling sample can be dangerously distracting.

The Times found dozens of examples of crashes where performing a rolling test was apparently distracting enough to cause an accident. For example, one man provided a clean sample, but dropped the device on the floor of his truck. When he panicked and tried to retrieve it, he slammed into another car and killed the occupant.

The good news is that, when states mandate ignition interlocks after every drunk driving conviction, some research indicates that there are up to 15% fewer fatal drunk driving accidents overall. Unfortunately, it’s not clear how common it is for ignition interlocks to cause deadly distractions.

Nevertheless, mandating the devices continues to be extremely popular at the state level, and there has been discussion of requiring them on all new cars sold in the U.S.

One reason, perhaps, why they are popular is that they promise to cut down on drunk driving at little or no cost to the public. In states like Tennessee that mandate the device after a DUI conviction, the offender ends up paying the cost. There is an installation fee and monthly monitoring fees, usually topping $1,000 a year in total.

Can we say they come at no cost to the public when they may be causing unnecessary accidents, though? As the Times points out, the National Highway Traffic Safety Administration (NHTSA) has expressed concerns about the necessity of the rolling retests, arguing that drivers should be required to pull over in order to perform the test. Pushback from manufacturers kept those concerns from being incorporated into official guidance on ignition interlocks.

Yet every interlock manufacturer recommends drivers to pull over to perform a retest.

Do you think drivers should be required to pull over in order to perform a retest? Are there hidden dangers to the devices that aren’t being considered?

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