How does marijuana impairment affect driving ability?

Cannabis may be legal for recreational use in California, but driving under its influence is illegal. Being high from marijuana impairs cognitive and motor skills, causes impaired driving and increases the risk of a car crashes.

Unlike alcohol, there is no “per se” concentration level of impairment for marijuana that would make a person legally too stoned to drive. However, if someone is pulled over for suspicion of driving under the influence of marijuana, an officer may administer a field sobriety test.

Marijuana use impairs several cognitive functions including, reasoning, short-term memory, attention span and motor coordination. According to the National Highway Transportation Safety Administration, marijuana use impairs driving performance significantly for one to two hours after use and increased the risk of getting into a car crash by 25 to 35 percent.

Impairments of driving under the influence of marijuana include:

  • A delay in the driver’s reaction time. This reduces the ability to respond quickly to things like traffic lights, unexpected pedestrians or unanticipated events.
  • A driver who has smoked pot may consciously overcompensate while driving. This can result in driving too slowly or keeping too much distance between vehicles.
  • A compromise in the driver’s attention span and concentration. This can limit the ability to be aware of and react to various sources of information at once.
  • The driver has poor lane positioning. The driver may weave in and out of lanes more and have more difficulty judging distance accurately while driving.

Marijuana use also affects a person’s ability to judge their own level of impairment. So, while someone may think that they are capable of driving, they may be more impaired than thought.

The penalties for being convicted for driving under the influence of marijuana are almost identical to drunk driving. They include license suspension, jail time, mandatory safe classes, and thousands of dollars in cost.