Cannabis and Driving

As more states in the U.S legalize recreational and medicinal cannabis, rates of driving under the influence of this drug are increasing significantly. Aspects of this emerging public health issue potentially pit science against public policy. The authors believe that the legal cart is currently significantly ahead of the scientific horse. Issues such as detection procedures for cannabis-impaired drivers, and use of blood THC levels to gauge impairment, should rely heavily on current scientific knowledge. However, there are many, often unacknowledged research gaps in these and related areas, that need to be addressed in order provide a more coherent basis for public policies. This review focuses especially on those areas. In this article we review in a focused manner, current information linking cannabis to motor vehicle accidents and examine patterns of cannabis-impairment of driving related behaviors, their time courses, relationship to cannabis dose and THC blood levels, and compare cannabis and alcohol-impaired driving patterns directly. This review also delves into questions of alcohol-cannabis combinations and addresses the basis for of per-se limits in cannabis driving convictions. Finally, we distinguish between areas where research has provided clear answers to the above questions, areas that remain unclear, and make recommendations to fill gaps in current knowledge.

Decision Strategies while Intoxicated relate to Alcohol-Impaired Driving Attitudes and Intentions

Objective: Approximately 28 million individuals engage in alcohol-impaired driving (AID) every year. This study investigated individuals’ AID decision making strategies under intoxication, their variability across the breath alcohol concentration curve (BrAC), and the association between strategy and AID attitudes and intentions. Method: 79 adults (23.9 years, 57% women) who drank alcohol ≥2 days per week and lived >2 miles away from their typical drinking locations completed an alcohol administration protocol and AID decision making task. AID attitudes, intentions, and behaviors were assessed repeatedly across the BrAC curve. Bayesian cognitive modeling identified decision strategies used by individuals on the AID decision making task, revealing whether alcohol consumption level and/or ride service cost factored into individuals’ decisions to drive while impaired or obtain a ride. Additional analyses tested whether AID attitudes and intentions were related to individuals’ decision strategies. Results: Two decision strategies were examined on the ascending and descending limb of the BrAC curve: compensatory (both consumption level and ride service cost factored into AID decisions) and non-compensatory (only consumption level factored into AID decisions). Switching to a compensatory strategy on the descending limb was associated with lower perceived intoxication, perceiving AID as less dangerous, and being willing to drive above the legal BrAC limit. Conclusions: Results suggest that risk for engaging in AID is higher for those using a cost-sensitive, compensatory strategy when making AID decisions under intoxication. Future research is needed to test whether AID countermeasures (e.g., subsidized ride services) are differentially effective according to decision strategy type.

Everything Is Bigger in Texas: Alcohol Impaired Driving in Houston (2014–2018)

Driving while intoxicated (DWI) or driving under the influence of drugs (DUID) poses a continued public safety risk in Texas, which has one of the highest alcohol impaired traffic fatality rates. This study aimed to identify alcohol and drug use trends seen in DWI/DUID cases in the city of Houston from 2014 to 2018 to better understand the populations at risk. Blood samples submitted to the Houston Forensic Science Center (HFSC) were evaluated for blood alcohol concentration (BAC), drug concentrations and demographics. During the 5-year period, 12,682 Houston driver blood samples had a mean (median) BAC of 0.151 g/dL (0.167 g/dL) and age of 36.3 (34) years. Fifty percent of samples were white males. Seventy-five percent of samples were individuals aged 21 to 44 years. Between 2014 and 2018, the number of cases submitted nearly doubled, from approximately 2,000 cases per year to over 3,700. In 2014, 23% of cases submitted required further analysis per HFSC testing policy (drug screen and confirmation for DWI/DUID cases when BAC < 0.100 g/dL), which rose to 27% by 2018. Of those, 36% were polydrug cases, requiring two or more confirmation tests. Cannabinoids was the most common drug class detected (34% of cases analyzed for drugs), followed by benzodiazepines (25%), phencyclidine (20%), cocaine/metabolites (15%) and opioids (12%). Phencyclidine rose from the fifth-most commonly detected drug in 2014 to the second-most drug in 2018. Only 3% of all cases (n = 408) were negative for both alcohol and drugs. Communication between law enforcement and laboratory management is recommended to address growing caseload more effectively. The study limitations (e.g., limited scope of analysis) suggest the present data underestimated the full extent of impaired driving in Houston, indicating even more urgent needs for increasing resources and efforts to reduce this serious threat to public safety.