The California Department of Motor Vehicles (DMV), in partnership with the California Highway Patrol (CHP) and the University of California, San Diego, are looking for 300 volunteers from the Sacramento area for a study to test various methods to detect cannabis-impaired driving.
Volunteers must be between the ages of 21 and 55, possess a valid California driver’s license, be a current cannabis user willing to abstain from cannabis use prior to participation, and live within approximately 15 miles of the CHP Academy in West Sacramento. Volunteers who are selected for the study will receive up to $150 for their participation. The US Food and Drug Administration-approved research project is set to begin in August.
Those interested in participating in the study can find out more today on the DMV website. Potential volunteers will be asked to complete a preliminary screening questionnaire. The goal of this study, expected to last between nine and 18 months, is to determine how well these methods detect cannabis-impaired driving and to help identify new indicators of this kind of impairment.
Most cannabis drivers are not impaired
Cannabis affects driving in ways that are distinct from other substances, such as alcohol. While having a blood-alcohol content (BAC) of greater than 0.08 percent is sufficient to conclude that a motorist is not able to safely operate a motor vehicle, no comparable number exists for cannabis. Numerous studies show that people with even high levels of cannabinoids in their systems are not functionally impaired. In fact, impairment is more frequently linked to cannabis naivety than to high THC levels in the blood.
“Working in collaboration with our traffic safety partners and key stakeholders on this groundbreaking study will provide potentially lifesaving information, resulting in safer roadways in California for all who use them,” said CHP Commissioner Sean Duryee.
In the last three years, California has reported an increase of 62% in the number of fatal crashes involving people with drugs (including cannabis) in their systems, from 173 in 2018 to 280 in 2021. Other states showed a reduction in fatal accidents after legalization. The data collection only shows if someone in a vehicle had cannabis or other drugs in their system, not whether they were impaired or even if it was a merely passenger who was high.
Current blood and urine tests can show the presence of cannabis, and saliva tests can suggest how recent use was, but none show whether cannabis negatively affects the driver. The lack of accurate data underscores the importance of research to better understand how, if and when cannabis and other drugs impair driving and to establish best practices for detecting drug-impaired drivers.
Double-blind study
The study will include random double-blind assignment of substance. Participating drivers will receive either a real cannabis product, a placebo, or no substance. This means that neither participants, researchers nor officers involved in the study will know whether a driver consumed active cannabis at the time of that driver’s participation.
Participating drivers will operate a vehicle within a safe, closed-course environment at the California Highway Patrol Academy in West Sacramento, rather than a driving simulator. The vehicle will be equipped with instruments that record driver actions and vehicle movements.
Study design could bias its interpretation
This process appears to build in a bias against cannabis users, who have been shown to make more adjustments as they drive, even though there is no demonstrated correlation between frequency of adjustments and safety of driving.
Every correction made by the driver to the steering wheel, changes in acceleration and braking, as well as the vehicle’s position to the accuracy of two centimeters will be measured multiple times per second. Some are concerned that this hyper-detailed approach is likely to generate micro-data that looks frightening to the lay person or legislator but does not reflect the macro outcome of safe overall driving performance.
One study co-sponsor, the CHP, has a decades-long history of enforcing marijuana prohibition while opposing adult cannabis legalization and even medical marijuana. Its agents still regularly arrest people for allegedly driving cannabis-impaired but proving the case is very difficult. With the help of an attorney and a good cannabis expert witness can often get charges reduced by having the accused plead to a lesser, included offense.
The current enforcement of cannabis (and other drug) impairment relies on behavioral methods of detecting impairment. These include the various cues that law enforcement officers are trained to look for, including erratic driving behaviors, field sobriety tests and an additional evaluation from a Drug Recognition Expert (DRE) to determine the substance(s) causing impairment.
This study is being conducted using funds allocated to the CHP for research on cannabis-impaired driving under Senate Bill 94 (2017). The Research and Development Branch of the DMV is conducting this study in collaboration with CHP and the Center for Medicinal Cannabis Research at the University of California, San Diego.