Are High Drivers High Risk?

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The danger of driving under the influence of alcohol (DUI) has been solidified for some time. The development of DUI laws and enforcement has been grounded in scientific research about crash risks and the effects of alcohol are easy to measure. However, driving under the influence of marijuana (DUIM1) presents an entirely different issue. It may not be wise to assume that similar laws, tests, and enforcement methods should apply. If there is anything to take away from the body of DUI policy, it is that it was developed to decrease accidents rather than indirectly prohibit alcohol. If marijuana is to be legalized, there is likely to be an increased level of enforcement to prevent the dangers of DUIM. However, such enforcement is only necessary if these dangers actually do exist.

DUIM is a criminal offense in California and will continue to be even if marijuana is legalized.2 A California roadside survey conducted in 2012 found that 7.4% of drivers tested positive for some amount of THC, a psychoactive component found in marijuana. To put that into perspective, 7.3% of drivers tested positive for alcohol. Although the occurrence of intoxicated drivers may be almost identical for alcohol and marijuana, the similarities quickly diverge when it comes to the crash risk these drivers present. DUIM after legalization is only an issue if high drivers actually present a danger to themselves and society.

The National Highway Traffic Safety Administration (NHTSA) recently released the results of a study that was “the largest and most comprehensive study to address alcohol and drug crash risk in the United States.” This study was conducted in 2012 over a 20-month period in Virginia and tested thousands of drivers using blood, urine, and saliva for the presence of THC. The NHTSA took care to match characteristics of control drivers with those of crash-involved drivers as closely as possible. These characteristics included age, gender, ethnicity, and alcohol use. When the variables of age, gender, ethnicity, and alcohol use were not accounted for, the results showed an increase in crash risk for those who tested positive for THC. However, when the analysis accounted for these variables, the correlation vanished – the NHTSA study did not find an increased crash risk associated with THC use. In contrast, drivers at a .08% blood alcohol level (the legal limit in every state) had about four times the chance of crashing.

The NHTSA study is the first large-scale study of its kind conducted in the United States, and so it stands to be the best indicator of an actual, observable crash risk for DUIM in California. The study found no increased risk, and it calls into question whether increased enforcement is actually necessary. This leads one to wonder how these results are even possible. Marijuana is a psychoactive drug, and an analysis of numerous studies (Sewell) “concluded that marijuana causes impairment in every performance area that can reasonably be connected with safe driving of a vehicle, such as tracking, motor coordination, visual functions, and particularly complex tasks that require divided attention[.]” Despite these effects, the Sewell analysis found that most marijuana intoxicated drivers show only small impairments on actual road tests while more experienced marijuana users showed almost no functional impairment.

The study attributes these results to evidence that marijuana intoxicated drivers are are able to compensate for the effects of their intoxication. For example, they will drive slower, increase their distance from cars, and try to overtake less. On the other hand, alcohol intoxicated drivers will underestimate their impairment, and will even drive more aggressively compared to sober drivers. A year after the Sewell analysis, a study was completed that seems to agree with their findings. In 2010, a double-blind, placebo-controlled study of 21 heavy cannabis users was conducted, rating each individual’s performance on tasks that tested their ability to track, make quick decisions, multitask, and react to a stop. This study found that marijuana generally did not affect task performance, concluding that “heavy cannabis users develop tolerance to the impairing effects of THC on neurocognitive task performance.”

These studies help explain the surprising results of the NHTSA study, and together, they show that DUIM may not be the public safety hazard that it is often thought to be. However, there are concerns that legalization will change the landscape of marijuana use, causing both an overall increase in DUIM related crashes, along with an increased crash risk by creating new users who are unable to successfully compensate for their intoxication. This concern is not without merit, but it cannot be expressed with certainty either.

The DMV has found that out of fourteen states that have allowed access to medical marijuana, three of them showed an increase in DUIM crash rates from the time of access to 2009. California was one of these states, showing an increase in 2.1 percentage points for fatal crashes where a driver tested positive for marijuana intoxication. This may seem insignificant, but it was a 196% increase. However, this uptick occurred in 2004 when medical marijuana was initially decriminalized, and there was no significant growth for 6 years after. From these results, the DMV suggested that medical marijuana is simply providing more access to a stable population of patients rather than creating new users. If the effect of legalization is to follow the same pattern, it will not create an explosion of new, inexperienced users, but it will increase access for experienced users, the ones who have shown the ability to drive safely in experiments and studies.

More importantly, if the goal of DUIM policy is to reduce crash risk, an increase in the total number of DUIM related crashes does not show that there is an increased risk of crashing. The DMV study explicitly states that determining the crash risk of DUIM was neither the intent nor purpose of the study. Accident totals were not adjusted for the increased use of marijuana in states where medical marijuana was allowed. Greater access to marijuana increases the number of people who are intoxicated, and when those people get into accidents, there is an increase in accidents involving marijuana intoxicated drivers. Confused? Here is an analogy: If there is greater access to yellow shirts, then an increase in accidents involving drivers in yellow shirts is likely to occur (provided that people want to wear yellow shirts). It does not follow that wearing a yellow shirt causes accidents, and similarly, the DMV results establish nothing about the actual risk of crashing.

The NHTSA study, on the other hand, was purposefully designed to discover such risk, and it found that drivers intoxicated on marijuana do not have a heightened risk of accidents compared to sober drivers. If the goal of DUIM policy is to reduce accidents, there must be a heightened risk to reduce. Even if marijuana is legalized, it cannot be assumed that an increased crash risk will come along with it.

It would be a shame to make the trek through all this technical, scientific data for it to merely be an academic exercise. But it unfortunately is. Questioning the necessity of increased enforcement will likely be nothing but a philosophical pursuit. It is almost assured there will be an increased focus on DUIM enforcement whether it is useful or not. In reaction to marijuana legalization, Colorado and Seattle have enacted new DUIM laws, funded training programs for their officers, and instituted new field tests for discovering marijuana intoxicated drivers. While California still awaits legalization, counties such as Los Angeles have already taken similar steps in officer training and field-testing. With legalization comes enforcement, and the state will have to design policy and procedure to prevent DUIM in a fair and just way. Many of us will also have to find a way to forget that our tax dollars are being spent on a problem that may not exist.

1. I choose to use the term DUIM here instead of using the more common term of driving under the influence of drugs (DUID). DUID is often the term used for marijuana intoxicated driving under the California Penal Code. This is because the pertinent section of the code does not distinguish between drug types other than alcohol, so all non-alcohol intoxication can be referred to as DUID. For this reason, I choose to use DUIM in order to specify that I am only talking about marijuana intoxication and not the countless other drugs that DUID can refer to.
2. California Penal Code section 23152(e)

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