People who use marijuana may feel that it does not affect their driving ability, but research shows otherwise. According to AAA, marijuana is the second-most common impairing substance among drivers after alcohol.
Marijuana does not affect drivers exactly the way that alcohol does, but it still has an effect. It is against the law to drive while intoxicated or impaired by any substance, regardless of its legality.
How much marijuana is safe while driving?
THC is the psychoactive chemical that makes marijuana intoxicating. Research has yet to discover a specific level of THC in the body at which driving impairment occurs. One person may have no impairment after consuming THC in large amounts while another may show significant impairment after consuming smaller amounts of THC. The safest assumption is that any marijuana in the system is unsafe for driving.
How does marijuana affect driving ability?
Marijuana can affect driving ability in multiple ways. It appears to have the biggest effect on routine, reflexive driving tasks. When a driver is under the influence of marijuana, he or she suddenly has to think about performing actions that would ordinarily come automatically. This slows down reaction time.
Marijuana also negatively affects physical function, cognitive processing, coordination and attention, all of which are necessary for operating a vehicle safely. In practical terms, these effects can cause a driver to deviate from his or her lane more often or drive at speeds so slow as to be unsafe.
Since 2007, government surveys have shown increased reporting of cannabis use by drivers, particularly by those driving during the weekend or at night.