An “ignition interlock device” (IID) is a device that can be installed in a car which prevents the car from operating if the driver has alcohol on his breath. In order to turn on the car, the driver must first blow into the IID, which detects breath alcohol.

In 2010, a pilot program was begun in four California counties. Since July 1, 2010, in those four counties – Alameda, Sacramento, Tulare, and Los Angeles – all drivers convicted of DUI have been required to install an ignition interlock device in their cars. The pilot program lasts until January 1, 2016 at which time it will expire unless reenacted.

Meanwhile, the California legislature commissioned a study in order to test the effectiveness of ignition interlock devices in the pilot counties. The understanding was that whether or not IIDs should be made mandatory for persons convicted of DUIs would depend on the experience in the pilot counties.

This year, the Research and Development Branch of the California Department of Motor Vehicles completed the study. The results of the study are surprising. According to the official DMV bulletin summarizing the report: “The IID pilot program was not associated with a reduction in the number of first-time and repeat DUI convictions in the pilot counties. In other words, no evidence was found that the pilot program has a general deterrence effect.”

The authors of the study propose yet another study, this one looking at whether or not IIDs caused “changes in the specific behavior of individual drivers.” It is not clear how this study would differ from the current study. The current study compares the rates of DUIs in the pilot counties before and after the mandatory ignition interlock device program and finds no change. What is clear is that unless there is actually data showing that IIDs reduce drunk driving, drivers convicted of DUIs should not be forced to install ignition interlock devices. Getting a DUI is already costly enough. This requirement would be especially burdensome for low-income drivers.