Thursday, June 6, 2019
Last month, the Congressional Research Service released this interesting short report titled simply "Marijuana Use and Highway Safety." Here is its introduction:
A growing number of Americans report that they use marijuana. As more states decriminalize the use of marijuana, the question of what impact marijuana usage has on the risk of a driver being involved in a motor vehicle crash has become more pertinent. In a survey, the majority of state highway safety offices rated drugged driving an issue at least as important as driving while impaired by alcohol.
When faced with the issue of driver impairment due to marijuana, some stakeholders tend to approach the issue using the analogy of driver impairment due to alcohol. However, there are important differences between the two substances. The fact that alcohol reduces a user’s ability to think clearly and to perform physical tasks has been known for decades. Extensive research has established correlations between the extent of alcohol consumption and impairment, including drivers’ reaction times. Much less research has been done on marijuana. Marijuana is a more complex substance than alcohol. It is absorbed in the body differently from alcohol; it affects the body in different ways from alcohol; tests for its presence in the body produce more complicated results than tests for the presence of alcohol; and correlating its effects with its levels in the body is much more complicated than for alcohol.
That marijuana usage increases a driver’s risk of crashing is not clearly established. Studies of marijuana’s impact on a driver’s performance have thus far found that, while marijuana usage can measurably affect a driver’s performance in a laboratory setting, that effect may not translate into an increased likelihood of the driver being involved in a motor vehicle crash in a real-world setting, where many other variables affect the risk of a crash. Some studies of actual crashes have estimated a small increase in the risk of crash involvement as a result of marijuana usage, while others have estimated little or no increase in the likelihood of a crash from using marijuana.
This CRS report addresses various aspects of the issue of marijuana-impaired driving, including patterns of marijuana use, the relationship and detection of marijuana use and driver impairment, and related state law and law enforcement challenges. The report also references the congressionally required July 2017 report by the Department of Transportation’s National Highway Traffic Safety Administration (NHTSA), Marijuana-Impaired Driving: A Report to Congress (hereinafter referred to as NHTSA’s 2017 Marijuana-Impaired Driving Report to Congress), as well as other studies and research.