Vehicle operation by persons under the influence of alcohol is a well known safety problem in the United States and throughout the world. Thousands of deaths per year in the United States are attributable to drivers operating vehicles under the influence of alcohol. To address this problem, most states have established laws that prohibit operation of a vehicle by an individual with a blood alcohol content (BAC) greater than a preset value (e.g., 0.08% BAC). In addition, “ignition interlock” systems have been developed which are directly connected to a vehicle's ignition system and are designed to prevent vehicle operation by inebriated individuals. Many states require the installation of ignition interlock systems in the vehicles of individuals convicted of driving under the influence of alcohol, particularly repeat offenders.
Conventional ignition interlock systems include a breath analyzer which measures the alcohol content of the breath of an individual. It is well known that the alcohol content of gas present in the alveoli of the lungs has an alcohol content directly proportional to that of the bloodstream of an individual. Blood alcohol content, thus, can be accurately determined by measuring breath alcohol content with a breath analyzer.
Typically, in order to start a vehicle equipped with an ignition interlock system, the driver must first blow into the breath analyzer. If the driver's breath alcohol exceeds a preset limit, the vehicle's ignition is disabled and the vehicle is rendered inoperable. If the driver's breath alcohol is below the preset limit, ignition is permitted and the vehicle may be started. If a driver successfully passes an initial breath test and is allowed to start a vehicle, some ignition interlock systems will require one or more retests (typically random) of the driver after vehicle ignition. These retests may occur as the driver is operating the vehicle (referred to as “rolling retests”) or the driver may be required to stop the vehicle prior to taking the retest. If the driver either refuses to take a retest or if the driver's breath alcohol exceeds a preset limit, vehicle operation may be disabled or may become disabled within a preset period of time. Exemplary ignition interlock devices that utilize breath analyzers are described in, for example, U.S. Pat. Nos. 3,780,311; 3,824,537; 3,831,707; and 4,592,443.
Operation of conventional ignition interlock systems is unsupervised. This lack of supervision has led to various attempts to bypass the breath analyzer such as by using air or other gases from balloons, bicycle pumps, gas station air hoses, and other sources. As a result, conventional ignition interlock systems may include breath temperature and humidity detection sensors to deter the use of non-human breath samples.
The lack of supervision has also led to attempts by vehicle operators to circumvent ignition interlock devices by using breath samples of non-driving individuals. To deter a person other than a vehicle operator from taking a breath test in order to start a vehicle, conventional ignition interlock systems have utilized various ways for confirming the identity of the person providing the breath sample. For example, the use of retina scans, voice identification, and face recognition have all been utilized. See, for example, U.S. Patent Application Publication Nos. 2002/0089660, 2002/0084130 and 2002/0117287. Unfortunately, many of these systems are complicated and expensive.
Accordingly, there exists a need for a cost effective and reliable ignition interlock system that is capable of discriminating, without human supervision, between a vehicle operator and other persons in order to prevent circumvention of the ignition interlock system.