State Laws, Industry Attention Needed to Advance Roadside Marijuana Testing for Drug-Impaired Driving

With the movement to legalize marijuana use for medical or recreational purposes gaining traction, states are calling for improved standards for marijuana testing, particularly as it relates to measuring drivers' drugrelated impairment. But, the association between legal definitions of detection and the capabilities of tests to judge impairment is complex and not fully understood.

Medical marijuana is legal in 23 states in the U.S., while recreational use of the drug is legal in Alaska, Colorado, Oregon, Washington, and Washington, D.C. An additional 16 other states have decriminalized possession of small amounts of marijuana. This changing legal landscape, combined with recent studies assessing the prevalence of drivers with detectable drugs in their blood, indicate that an increasing number of drivers are using marijuana. But, local and state law enforcement departments don't have the necessary tools and standards to determine if drivers are impaired.

In response to growing drug use, states have implemented piecemeal regulation for impairment testing. According to the Governors Highway Safety Association (GHSA):

• Nine states have zero tolerance for delta-9-tetrahydrocannabinol (THC), the psychoactive ingredient in cannabis or metabolites.

• Three states have zero tolerance for THC but no restriction on metabolites.

• Five states have specific per se limits for THC (Pennsylvania, 1 ng; Nevada and Ohio, 2 ng; Montana and Washington, 5 ng).

• Colorado has a reasonable inference law for THC.

• The majority of states, including Oregon, have no marijuana-specific laws and rely on police officers' observations.

Forty percent of fatally injured drivers test positive for drugs and 22 percent of all drivers tested in the National Highway Traffic Safety Administration's (NHTSA) 2013-2014 National Roadside Survey of Alcohol and Drug Use by Drivers would test positive for at least one drug. In both studies, marijuana is the most common drug detected, but testing only detected the presence of THC, not the quantity of the drug. Also, both surveys found the presence of marijuana increasing in frequency, but again, could not link the presence of the drug to either impairment or the cause of the fatal crash.

Test Results to Define Impairment
GHSA's report, Drug-Impaired Driving: A Guide for What States Can Do, makes recommendations for both state and federal action against drug-impaired driving, including continued research on the effects of drugged driving laws and the level of impairment produced by different concentrations of the most commonly used drugs. This lack of a clear link between impairment and drug concentrations in the body makes it difficult to define drug impairment, which, in turn, challenges efforts to enforce drug-impaired driving laws and standardize testing.

Many long for the marijuana analogy to a blood alcohol level, but evidence suggests this may be impossible. Compared to alcohol, defining and identifying impairment due to drugs is more complicated. In experimental settings, marijuana has been shown to impair psychomotor skills and cognitive functions associated with driving, including vigilance, time and distance perception, lane tracking, motor coordination, divided attention tasks, and reaction time. However, detection of the drug's presence in the body, its concentration, and its impairing effects are not well understood and can vary by person due to frequency of use and individual differences in metabolism.

The height of intoxication and related impairment doesn't occur when blood THC levels peak. Experts say that a few hours after smoking marijuana, a user could still be intoxicated, yet pass a drug-related driving test because only small traces of THC would be in the blood. With edible marijuana, blood THC levels would be even lower, even when the user is still high. In contrast, frequent users have so much THC built up in body fat (THC is fat soluble, as opposed to alcohol, which is water soluble), it would leach out of body fat into blood for weeks reaching moderate levels, even when users are not actively high.

Steps to Improve Testing
Additional recommendations from GHSA's Drug-Impaired Driving: A Guide for What States Can Do focus on efforts to improve testing, including testing all fatally injured drivers, standardizing testing protocols and procedures for roadside testing and laboratory testing, and validating roadside testing devices. These efforts, GHSA says, will need to be informed by further research on the effects of drugs on driving; the effectiveness of drugged driving per se laws; the accuracy, reliability and cost-effectiveness of drug detection tests; and the feasibility of establishing national standards for various controlled substances involved in drug-impaired driving.

"An accurate, reliable, and inexpensive oral fluid test device that could be used at the roadside would be very useful. It should be quick and easy to use and should detect the most common drugs that impair drivers," writes GHSA in its report. "If an oral fluid test were of evidential quality for some drugs it might reduce the need for blood tests. Research is needed to continue refining, evaluating, and eventually establishing standards for oral fluid test devices. Continuing research is [also] needed to determine if a useful marijuana breath test device can be developed."

Additionally, there are calls to establish national drug testing best practices that will include threshold concentrations, in addition to drug presence. National standards for toxicology testing would also include identifying the circumstances under which tests should be conducted, a minimum set of drugs for which to test, and cutoff values for reporting the results.

Internationally, roadside drug testing is catching on in Australia and the United Kingdom, despite remaining uncertainties if detected drugs are actually affecting driving abilities. Experts say oral fluid testing is advantageous because improved timing of sample collection can provide results that more accurately reflect the driver's drug levels while driving. In addition to a lack of timeliness, current testing is plagued by inconsistent usage, expense and laboratory backlogs that often prevent results from being available in time for court appearances.

Takeaway: Roadside testing for marijuana is needed at a time when driving under the influence is increasing. Yet, development of these tests and adoption is hampered by non uniform testing standards and legal thresholds, as well as the current inability to differentiate the presence of a drug from impairment. Yet, officials are hopeful that a quick, noninvasive, and inexpensive roadside test can be developed soon.