Most people will tell you it’s a very bad idea to drive a car after consuming intoxicating substances like alcohol, and many opponents of legalizing marijuana in Massachusetts say doing so would only make the roads more dangerous.
But there’s still plenty of legal and scientific uncertainty around how much of an effect easier access to marijuana has had on drugged driving and serious accidents in the states where it’s been legalized.
Voters will hit the polls Nov. 8 to decide whether adults over 21 should be able to possess, consume, grow and sell marijuana in Massachusetts. Driving under the influence of drugs would still be against the law.
In places where marijuana is already legal — Colorado, Washington, Oregon, Alaska and Washington D.C. — the data’s not entirely clear on the impact that status has had on drugged driving and traffic accidents, but at least one state, Washington, where marijuana has been legal since 2012, has measured an uptick.
The fear by some in Massachusetts is that easier legal access to pot will lead to more impaired driving, especially if there’s no good way to test for criminal-levels of marijuana-caused impairment.
Studies say...The AAA Foundation this year released a study that examined data from Washington to see how often marijuana use was a factor in fatal crashes between 2010 and 2014. The reported data relied on blood testing for the presence of delta-9-tetrahydrocannabinol, the main psychoactive chemical in marijuana, in the involved drivers.
Between 2010 and 2013, an estimated 7.9 percent to 8.5 percent of drivers involved in fatal crashes tested positive for THC, but those numbers nearly doubled in 2014, the study shows.
The analysis included 3,031 fatalities, 48.5 percent of which had usable toxicology reports. The prevalence of THC among the rest of the sample was statistically estimated.
It found an estimated 10 percent of the drivers involved in such crashes had detectable THC in their blood at the time of, or shortly after, the crash during the time period examined. But most of them also had other intoxicating chemicals in their blood. Of that 10 percent, 34 percent had only THC in their system, while 39 percent had both THC and alcohol, 16.5 percent had other drugs in addition to THC, and 10.5 percent had alcohol, THC and other drugs present.
Impairment hard to show The study also noted the data provided could not determine whether a driver who tested positive for THC was actually impaired at the time of the crash, or if it was their fault.
In another study published in May, AAA found that there’s no truly reliable method to detect marijuana impairment in a driver, and encouraged police to rely on specially trained officers using field tests to establish impairment instead of laws linked to blood level tests.
“There is no evidence from the data collected, particularly from the subjects assessed through the Drug Recognition Expert exam, that any objective threshold exists that established impairment, based on THC concentrations measured in specimens collected from cannabis-positive subjects placed under arrest for impaired driving,” the study concluded.
It said the drug profile in the blood for water-soluble drugs like alcohol that have a long half-life roughly mirrors the way it distributes into the central nervous system, which means it gives a good representation of what the concentrations are like in the brain.
For drugs like THC that are fat-soluble, the drug is taken up rapidly into the brain and other fatty tissues where it concentrates, while the concentration in the blood drops rapidly. That means the blood tests aren’t a good measure of the effect of the drug on the user after more than a few minutes, according to the study. Most of the time, there’s a gap between arrest and blood testing, the report said.
Different folks Tom Marcotte, a researcher at the University of California, San Diego’s Center for Medicinal Cannabis Research, said testing for the presence of marijuana is also problematic for establishing impairment because latent THC can linger in a person’s body beyond the time they could be impaired. Someone who consumes marijuana regularly could have a chronic low level of THC in their blood, he said, while an occasional smoker who is actually impaired at the time could show a low level, but still be impaired.
“Attempts to use blood levels are fraught with difficulty,” he said. “The real challenge is relating crashes from impairment to the presence of THC in the blood.” He and his team are currently working to establish more accurate measures of marijuana impairment, which could be adopted as standards for use by law enforcement.
“The practical reality of identifying, evaluating, arresting, and sampling suspected impaired drivers means that the THC concentration measured in the blood specimen reflects neither the concentration in the subject’s blood at the time of arrest, nor the concentration of active drugs in the brain,” the May AAA report read.
Typically, a 3.5 to 5 nanograms per milliliter THC blood concentration is considered comparable to a 0.05 percent blood alcohol concentration, and driving with a BAC of 0.08 percent or higher is illegal.
Washington’s law finds anyone who tests positive for a THC concentration of 5 nanograms per milliliter of blood within two hours of driving to be guilty of driving under the influence. It’s illegal for anyone under 21 to drive with any amount of THC in their system.
Colorado In Colorado, the picture isn’t as clear. Data is slow to come, and fatal traffic accidents have remained relatively flat, the Denver Post has reported.
A report published by the Rocky Mountain High Intensity Drug Trafficking Area — a collaborative effort among local law enforcement in Colorado — found marijuana-related driving incidents were up since legalization.
The report defines “marijuana-related” traffic deaths as any time marijuana shows up in a toxicology report, but does not exclude the possibility of the presence of other drugs or alcohol.
The 2015 report said the average number of marijuana-related traffic deaths increased 41 percent in the two years since recreational marijuana was legalized compared to the medical marijuana commercialization years, 2009 to 2012. Fatal accidents with marijuana as a factor in those years, the report said, were 48 percent higher than pre-commercialization years, which began in 2006.
No good data yet Daniel Rowland, a spokesman for Denver, Colo.’s Office of Marijuana Policy, said the data that does exist for Denver shows that marijuana-related DUIs represent a small subset of all DUI arrests in the city.
Between 2013 and 2015, he said, 73 of the 148 arrests for driving under the influence of drugs were for just marijuana — about 3 percent of the total 2,532 DUI arrests in Denver for that period.
Alcohol, he said, remains the most common substance, and most cases involving that substance have historically been prosecuted based solely on that. Once it was detected, he said, officials typically didn’t check to see if other substances were present. That means good baseline data on the presence of other drugs was not collected prior to legalization, making any sort of trend harder to measure.
“People have been driving drunk and stoned in Denver for years, but it wasn’t tracked for marijuana specifically until we realized we needed to track those metrics separately,” Rowland said. “The short answer is those numbers are very low for overall impaired driving.”
The state has trained more Drug Recognition Expert officers since legalization, he said.
Drugged driving is illegal, but hard to enforce Existing Massachusetts law says a driver impaired by any amount of marijuana could face civil and criminal penalties and fines, but it’s more difficult to accurately test for marijuana impairment than alcohol impairment, and harder to get a conviction in court. There’s no reliable test like a Breathalyzer for stoned driving.
Experts and proponents of the Massachusetts ballot question expect that technology or better tests like the one Marcotte, the UCSD professor, is working on, to be developed and readily available within the next few years. The question in Massachusetts includes no provisions on how operating under the influence of marijuana should be measured or prosecuted.
In Colorado, the DUI law has a 5 nanograms-per-milliliter limit for THC concentration that allows juries to infer that a person was operating under the influence and convict them. But Jay Tiftickjian, a Denver-based lawyer who specializes in OUI and has written books on the topic, said many dispute that enough research has been done to set a limit like that.
“There’s a lot of iffy science concerning where that inference should be set, if at all,” said Tiftickjian. “The National Highway Traffic Safety Organization that standardizes field sobriety tests, blood alcohol limits and other things says there’s not enough research at this time. Until we have enough confidence where we can set limits, there shouldn’t be limits.”
Many of the marijuana OUI arrests he sees result from routine stops where police catch a whiff of marijuana, while alcohol-related arrests more commonly arise from erratic driving, he noted.
Tiftickjian said Colorado has seen an increase in marijuana-related drugged driving arrests, but said that’s likely a product of stepped-up enforcement efforts amid legalization. He said the state doesn’t separate cases based on the substance involved either — it all falls under the DUI law.
“A lot of the stats might not really be accurate — if someone has a 0.25 blood alcohol level and 5 nanograms of pot, they’re calling it a marijuana case even though you’ve also got an alcohol case, and a pretty bad one,” Tiftickjian said.
Tiftickjian noted edible marijuana-infused products pose a unique concern, particularly among tourists. “I find they’re not used to the potency of the marijuana. What’s being sold around here is the highest quality, and there’s so many more methods of delivery. Sometimes they don’t have any tolerance or experience with it.”
You can reach Tom Relihan at:
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