In the U.S. today, there is a widely-accepted and clear national standard for what is considered too drunk to drive legally – a blood alcohol content (BAC) of 0.08% or higher. But while most people understand the dangers of driving while intoxicated and wouldn’t dare let their loved ones drive drunk, it’s unclear where to draw the line for driving while high.
Recreational marijuana use is currently legal in 11 states and growing, and medicinal cannabis use is currently legal in 33. But as legalization makes its way across the country, policymakers are still struggling to define how to measure marijuana impairment and the extent of impairment the substance causes behind the wheel.
The challenges of defining marijuana impairment
The affects of marijuana negatively impact a person’s ability to focus and slows a person’s reaction time. But at what point is someone too high to get behind the wheel?
While law enforcement can detect marijuana use with blood or urine tests, it doesn’t tell them when the individual used the substance or indicate their level of impairment. Traces of marijuana can remain in the human body for weeks after using, and how high a person is can vary by the amount consumed, its potency and the individual’s tolerance to the substance.
The limitations of existing policies
While the general consensus is driving while high is unsafe, states with existing policies for driving while high still have some pitfalls. Most of these laws measure intoxication by the amount of THC – the psychoactive ingredient in marijuana – in a person’s system.
A handful of states have zero tolerance laws, meaning a person cannot drive with any amount of THC in their system. This of course is problematic due to the duration THC can remain in the body.
Colorado defines marijuana impairment as having more than five nanograms of THC per millimeter of blood, however; there is no linear correlation between THC levels and impairment. Other states rely on law enforcement to perform field sobriety tests to determine whether a person is high. But field tests are subjective at best and racial biases could influence their results.
The bottom line
Until scientists and lawmakers establish a legal limit for marijuana impairment, knowing when a person is too high to drive remains unclear. If you want to stay safe on the road and avoid a potential DWI, it’s best to only to drive when you’re sober.