The spread of legalized marijuana is fuelling an ongoing debate on how smoking pot may affect driving safety. The two sides of the debate each cite studies of crashes that support their position.
The Insurance Institute for Highway Safety (IIHS) released a study that noted a three percent jump in collisions in Colorado, Oregon, and Washington after those states made marijuana legal. In contrast, a study published by the American Public Health Association (APHA), based on Washington and Colorado, concluded there was no association between legalized marijuana and reported crashes.
Another study, by the National Center for Biotechnology Information (NCBI), based on broad data on marijuana usage and driving, concluded that driving after using marijuana is risky, but less so than drinking and driving.
With more states, including California, having legalized marijuana use, and others considering the move, here’s a rundown of what’s known about smoking it and driving, and what restrictions and regulation legal-pot states have imposed.
What pot does
The active, intoxicating ingredient in marijuana is the compound known as tetrahydrocannabinol, or THC for short. Studies show that THC slows down reaction times in the body, and also diminishes coordination and the ability to solve problems rapidly. Depending on the individual, these effects last up to three hours.
Indeed, unlike the effects of drinking, the types and degree of impact from using marijuana are highly personal. Driving under the influence of alcohol reduces the ability of every drinker to safely drive, and increases the likelihood you’ll be involved in an accident. But the effects of driving after using marijuana range widely, because people vary widely in their tolerance for THC — and therefore in their level of intoxication from the drug.
A further complication to regulating marijuana intoxication involves measuring THC levels in the body. When a driver is pulled over for drinking, law enforcement officers can conduct a roadside test of intoxication through the use of portable breathalyzers that measure the presence of alcohol in the driver’s breath. There is currently no such testing equipment for officers to use if they pull over a driver suspected to be impaired from using marijuana. Instead, they must arrest the individual and transport him or her to a local hospital for blood testing.
Changes in driving laws
Despite the challenges posed by these issues, many states nonetheless have developed laws that address marijuana usage while driving. And just as marijuana legalization varies by state, so do these laws. Colorado, Montana, Nevada, and Washington are among the few states that use per-se limit laws, meaning that once individuals have a certain amount of THC in their body, it is illegal for them to drive. Other states rely on tests measuring the amount of marijuana metabolites — compounds that THC metabolizes into — in the driver’s blood or urine.
In addition to establishing usage limits while driving, states with legalized marijuana usage are finding the need to institute additional laws. For example, California has a law prohibiting the use of marijuana while driving or being a passenger in a vehicle. Meanwhile, states including Colorado are reinforcing their laws, and the claimed dangers of "drugging and driving," with a series of public service announcements, much like those for drinking and driving.
The sentencing guidelines for these laws stipulate repercussions for violators similar to those for DUI, including fines, incarceration, license suspension, probation and loss of a vehicle. The severity of the consequence depends on the number of previous offenses, whether an accident resulted, and the level of THC found in the driver’s blood level.
Once a driver is found guilty of driving under the influence of marijuana, auto insurance companies consider them a bigger risk. Depending on the company and offense, drivers may experience an increase in their auto insurance rates or policy cancellation.
Driving after using marijuana can decrease the individual's ability to make sudden decisions while traveling and increase the risk of an accident.
As the number of states legalizing marijuana for medicinal or recreational purposes rises, the debate over how legalized marijuana affects driving will continue. It is likely that over time, standardized tests will become available, and states will continue to create new legislation that limits driving while under the influence of pot in order to minimize accidents and fatalities.