Editorial: Driving while high hard to define

Published: 8/23/2016 11:03:18 AM

States have been racing to write laws that define what it means to drive under the influence of marijuana. The early birds seem to be getting it wrong.

Colorado and Washington, which legalized recreational use of marijuana, pegged the level of impairment at 5 nanograms of active tetrahydrocannabinol (THC) based on a set amount of blood. Pennsylvania set a 1 nanogram threshold; Nevada and Ohio opted for 2 nanograms.

All across the map, states are all over the map.

Lawmakers may be loath to admit it, but setting a specific impairment threshold with THC is not as clear-cut as it is with alcohol. The science is just not there yet. A study this year by the AAA Foundation for Traffic Safety explained in detail why that is so — and called for a national effort to determine what constitutes impairment from marijuana.

This is a timely question nationally — and here in Massachusetts, where voters will decide this November whether to join states that have legalized the recreational use of marijuana.

In an interview last week, Senate President Stanley C. Rosenberg noted that while he supports the right of adults to decide whether to use marijuana, he is concerned about how Massachusetts is going about this possible change. One of his points: The state is not prepared to police traffic safety due to impairment resulting from marijuana use.

On that, it is hardly alone. The General Accounting Office reported in 2015 that there are many reasons why determining driving impairment due to marijuana use is far more complicated than it is for alcohol. It is well established that a blood alcohol level over .08 percent affects a person’s ability to drive.

But with marijuana it simply isn’t simple. Impairment, the GAO noted, can be influenced by the number of drugs ingested, their combined use and their varying effects on individuals.

What’s more, impairment levels don’t necessarily rise and fall according to THC levels. One AAA study reviewed 5,300 cases of people arrested for operating under the influence of marijuana. It found that some drivers with more than 5 nanograms of THC in their blood passed field sobriety tests. In that study, the median level of THC was 4 nanograms — below the limit set by several states.

THC can remain in a person’s system for days and weeks. That means blood tests alone are unreliable. States that hold fast to THC blood limits risk convicting some people wrongfully, the AAA study said, while letting others not safe on the roads go free. It is already illegal in Massachusetts to drive while impaired due to use of marijuana, but the law doesn’t define what that means. Just this month, a Deerfield officer stopped a Greenfield driver at 1 a.m. after noticing the man going 15 mph under the speed limit and crossing the center line. The officer’s report noted bloodshot eyes and dilated pupils, and the man was charged.

But defense attorneys hunting for clients online boast that it isn’t hard to beat these arrests. One notes that some blood tests fail to distinguish between THC that has a psychoactive effect and another kind that does not. Legislatures across the country haven’t been paying enough attention to complexities here. As of this spring, 17 states had set laws limiting how much THC a driver can have in his or her bloodstream, according to the National Conference of State Legislatures.

Marshall Doney, AAA’s president and CEO, said people naturally want a clear limit for THC, but that just doesn’t work. “It’s simply not possible today to determine whether a driver is impaired based solely on the amount of the drug in their body.”

But given public safety risks due to expanded access to marijuana, it is easy to see why lawmakers are eager to enact measures.

In one AAA study, 53 percent of drivers admitted that if they took to the road within an hour of ingesting marijuana, they’d face increased risks of accidents. And not just minor ones. Another AAA study looked at fatal accidents in Washington state before and after it made marijuana legal in 2012. Of all the fatal crashes there from 2010 to 2014, 10 percent of drivers had THC in their blood.

For the first four years in that study, the percentage of fatal crashes involving drivers with THC in their systems ranged from 7.5 to 8.8 percent. In 2014 it more than doubled to 17 percent. The AAA is right. To be fair to all who use our roads, the U.S. needs a national standard based on science.


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