Many licensed drivers in Virginia have heard of ignition interlock devices, but they do not have a full understanding of how the devices work or when a person can be compelled to use one. Virginia's traffic code requires that any person who is convicted of a drunk driving offense must install an ignition interlock system on his or her motor vehicle for a period prescribed by the judge. In addition, the guilty party cannot operate any motor vehicle that is not equipped with an ignition interlock device. Both penalties last until any period of driving suspension has expired. The offender must provide periodic reports to the court demonstrating compliance with the court's order.
An ignition interlock device is intended to prevent a person who has a current blood alcohol content (BAC) greater than 0.02 percent from operating the motor vehicle to which the device is attached. The device works by analyzing a sample of the would-be driver's breath to determine the blood alcohol content.
The driver must breathe 1.5 liters of air into the interlock device before attempting to start the vehicle. The device then measures the driver's BAC. If it exceeds the limit of 0.02 percent, the vehicle will not start.
Assuming that the vehicle starts, the driver must perform "rolling retests" during the trip. If a test registers a BAC greater than 0.02 percent, the vehicle's lights will flash, and its horn will sound. Police know the signal and will investigate.
The offender must also maintain an electronic log of all driving activities. If the offender attempts to remove the interlock device, an alarm will sound, and the attempt will be recorded on the electronic log. The cost of installation of these devices must be borne by the offender.
Some people who have been ordered to use an ignition interlock device will continue to use one after their driving rights are restored. While an ignition interlock may seem to be cumbersome, the continuing use of a device is a convenient way to avoid an inadvertent DUI.