There are three distinct offenses under our state law governing operating a motor vehicle while intoxicated. Each of them requires proof of a different fact for a conviction to result.

The first illegal scenario is operating a motor vehicle while under the influence of a controlled substance or intoxicant or while under the influence of any medication or intoxicant that renders the driver incapable of driving safely. Proof of impairment is required for conviction, and this law, in one form or another, has been on Wisconsin books since motor vehicles were invented. Evidence includes law enforcement or other witness observations of driving behavior and field sobriety test results.

The second offense is based on any person driving or operating a motor vehicle with a prohibited blood alcohol concentration level. The current BAC measurement is 0.08, a percentage established in 2003, unless a person is a repeat offender or subject to an ignition interlock device order. In the latter cases, a lower threshold applies. What makes this second type of offense different from the first is that no proof of impaired driving is required for conviction. This is called a per se law, meaning an excessive BAC measurement itself is a violation of law.

In 2003 the third element of Wisconsin’s OWI law was added. It prohibits any person from driving or operating any motor vehicle with a detectable amount of a restricted controlled substance in his or her blood. As with the second type of offense, it’s the measurement itself that provides proof of the violation. A restricted controlled substance includes any that are specified as Schedule I controlled substances under the state’s controlled substances act. These would be drugs with serious potential for abuse and with no accepted medicinal use. Commonly abused drugs such as cocaine, methamphetamine and marijuana are included in this offense.

Someone may be charged with any combination of these violations within one incident. Conviction, however, can only apply to one basic OWI offense as a result of that occurrence.

Source: Wisconsin Legislative Fiscal Bureau, “Intoxicated Driver Laws,” accessed May. 28, 2015