What you need to know about legal pot and driving

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It’s already illegal to drive under the influence of marijuana. That won’t change under Prop 64, which aims to legalize recreational pot for adults 21 years and up. But if a lot more people use pot and get behind the wheel that could change safety conditions on California’s roads. So the question that’s going to be more and more important for law enforcement is: how high do you have to be to be considered impaired?

Will there be a legal limit for marijuana, like there is for alcohol?

Not for now. Lawmakers in Sacramento have debated a legal limit in the past and they could take it up again, but it’s not part of Prop 64. Colorado, Washington and other places where adults legally consume marijuana passed what’s called a “per se limit.” Drivers are allowed to have up to 5 nanograms of THC (the active compound in cannabis) in their system without being in violation of DUI laws.

Why can’t there just be a pot Breathalyzer?  

A lot of reasons. For one, THC is not water-soluble so it’s harder to measure than alcohol by unit in blood. It’s fat-soluble and you are the most high when you reach a peak concentration of THC in your brain. So, short of being able to test a driver’s brain tissue at the side of the road, there’s no good way to accurately capture the impairment of a driver. On top of all that, marijuana affects people very differently and a regular user can have a very high tolerance.

So how will police be able to tell?

Since California doesn’t have a “per se limit,” law enforcement looks for any sign of impairment (driving slowly, delayed reaction, swerving etc.) and then tests for any presence of THC to use in a possible prosecution. Police can ask to conduct a sobriety test, including a breath and blood test. If you’re placed under arrest for suspicion of DUI, police can order you to give a blood sample.

Some police departments already train officers to be “drug recognition experts.” If Prop 64 passes, the measure allocates $3 million a year to California Highway Patrol to conduct studies on detection of drug driving impairment from 2018 to 2023.

Have other states where pot is legal seen a rise in arrests or crashes?

There’s not a clear answer, because traffic violations and fatalities are often caused by many factors. But AAA research shows that in Washington using marijuana and getting  behind the wheel within the next few hours is a rapidly growing “contributing factor” to traffic fatalities. In Colorado, the number of DUI arrests for marijuana has jumped in the years since voters legalized recreational pot. In 2014, 12 percent of all DUI arrests were for marijuana. By 2016, the number of arrests for driving while high jumped to 20 percent. The increase could be a result of more people driving under the influence or just more police officers being trained for what to look for during stops.

Does marijuana actually make you a worse driver?

Most everyone agrees it does affect your driving (divided attention, lane tracking and cognitive function) and that it’s a bad idea to drive high. But there’s disagreement over just how dramatically marijuana impairs driving. One large-scale study by the federal government actually found no statistically significant risk associated with marijuana use, after adjusting for age and gender. Activities that appear to have a greater risk include: texting, taking prescription drugs, and eating while driving, according to the National Organization for the Reform of Marijuana Laws. But when alcohol and marijuana are combined, even low levels of intoxication can increase the risk of traffic crashes.

(Photo: versageek/Flickr)