Smoking marijuana became legal in Illinois on January 1, but driving while stoned is still illegal. Although impaired driving has legal consequences and may cause personal injury, proving that a driver is impaired by marijuana is difficult.
Drivers may not operate a vehicle while impaired by cannabis used medically or recreationally, according to the Illinois Secretary of State’s Office. Passengers cannot smoke marijuana in moving vehicles. While adults may legally possess one ounce of marijuana, it must be stored in the odor-proof and child-proof container that it was sold in.
A police officer who suspects that a driver is under the influence of marijuana may request that the driver undergo a field sobriety test. Police will likely look for signs of marijuana use, such as red eyes, drowsiness and slower response times. If there is probable cause after the driver takes the field test, the driver will be arrested and taken to a police station. Then, the driver will be asked to undergo a chemical test of breath, blood, urine or other bodily substance within two hours after being stopped. The person’s driver’s license will be revoked and criminal charges may be filed if the test is positive for over five nanograms of tetrahydrocannabinol, marijuana’s active chemical, per milliliter of blood or over 10 nanograms of another bodily substance. If the driver refuses this test, the driver’s license will be revoked.
But, this test may be inaccurate because THC may stay in a person’s body for weeks or even months. A frequent marijuana user may have over 100 nanograms of THC per milliliter of blood right after ingesting, which can remain elevated for weeks even if the user is no longer impaired or high.
There is no industrially recognized marijuana “breathalyzer” device. The five nanogram threshold was based upon the limit for drunk driving and may be inaccurate for marijuana users. However, a task force was created in Illinois to study driving under the influence of cannabis and must submit a report to the governor by July 1.