This fall, the Massachusetts Supreme Judicial Court considered whether field sobriety tests (FSTs) could be admitted as evidence when a police officer suspects the driver has been driving while under the influence of marijuana. In determining whether a suspect is driving under the influence of alcohol, police typically administer three FSTs — the “walk and turn test,” the “horizontal gaze nystagmus test,” and the “one leg stand test.” These tests were specifically developed to measure alcohol consumption, and there is agreement in the scientific community that a strong correlation exists between insufficient performance on the FSTs and a BAC (blood-alcohol content) of over .08% (the legal limit). By contrast, there is no scientific agreement yet that FSTs, or some FSTs, can determine marijuana intoxication.
In 2016, the Illinois governor signed SB 2228, dictating that drivers will be subject to Illinois marijuana DUI charges only if they have at least 5 ng of THC in their blood, or at least 10 ng of THC in their saliva. Prior to the law, the state could bring DUI charges even when the subject had just trace amounts of THC in their system. This meant that someone who smoked marijuana weeks prior could still test positive and be charged with a misdemeanor. The fact that people could face DUIs for trace THC in their systems “was making a crime without any criminal intent,” said an Illinois public defender.
The new Illinois law did not change the pre-existing law making it a DUI to drive while under the influence of cannabis. At trial, the state must prove by the arresting officer’s expert testimony that the person was impaired due to the consumption of cannabis. As with a DUI for alcohol, a person can be found guilty even if he or she is under the “legal limit” if the court finds that he or she was impaired to the point that he or she was unable to safely operate a motor vehicle.