Ignition Interlock Devices in DUI Cases

State legislatures have addressed the public safety problem of recidivist drunk drivers by authorizing various types of law enforcement tools. One such tool is the "ignition interlock" device, which attaches to the vehicle's steering mechanism and ignition. When used by the courts or state motor vehicle departments in conjunction with a monitoring, reporting, and support program, the ignition interlock system provides drunk driving offenders (driving while intoxicated (DWI) or driving under the influence (DUI)) with an alternative to full license suspension.

Forty-five states have some form of ignition interlock law, but fewer than half of them make ignition interlocks mandatory for repeat and chronic DWI/DUI offenders. In general, the statutory scheme allows a driver to voluntarily install this device at the driver's own expense. The participant is usually a habitual offender (e.g. a multiple offender within a define time period) who, after the expiration of a certain period, intends to apply for a restricted license upon proof of the installation of an interlock device.

The device requires a vehicle operator to blow into a small handheld alcohol sensor unit that is attached to a vehicle's dashboard. The car cannot be started if a blood alcohol content (BAC) is above a preset level (usually .02 to .04 BAC). The unit is programmed to allow another attempt after a certain time period (usually 30 minutes) has elapsed. Circumvention may be prevented by requiring a "humtone" at the same time the sample is given. That is, the driver must hum and blow at the same time. In addition to requiring a test to start the engine, the devices also require a test while driving. These are called "rolling" or "running" retests, and they are intended to keep drivers from having a sober friend start the car and then allow the intoxicated driver to take over the wheel. The retests require the driver to provide breath tests at random intervals while driving, occurring anywhere between 15 to 60 minutes after the ignition interlock device initially allowed the car to start. If a rolling retest is not successfully completed, or not taken at all, the computer device will record this, and it will result in a violation for that calibration period. It should be noted that is a misdemeanor crime to allow someone else to blow into the device.

Violation of the interlock system will result in termination from the program and suspension or revocation of the restricted license. A violation consists of several failed start-ups within a fixed period, failure to report to the installer for regular monitoring, repeated retest violations, and tampering or removal of the device.