Major findings 2010–2020

Some of our major findings from 2010 to 2020 are described below.

Alcohol

We’ve confirmed that alcohol significantly impacts the ability of drivers to control their vehicle if they have a blood-alcohol concentration of 0.08%^1,2 (legal limit) and also at 0.05%³ (as recommended by the National Transportation Safety Board). When looking at urban driving, we found that at 0.05% BAC, drivers tended to drive faster and had a harder time staying centered in their lane. However, they did not exhibit more frequent lane departures similar to what is seen with drivers above 0.08% BAC.³

Cannabis

When considering the impacts of cannabis on driving performance, our research has shown that following acute usage of inhaled cannabis, drivers had less vehicle control both laterally⁴ and longitudinally.⁵

Even when they were not under the influence of cannabis, regular cannabis users were found to drive differently than non-cannabis users. Young adult drivers who use cannabis—but were sober at the time of our study—drove slower but also steered significantly less often and used the gas pedal less often than drivers who did not use cannabis.⁶ This suggests that lasting effects of cannabis use persist and may lead to detrimental driving behaviors even after intoxication has subsided. These findings have implications for legislation in support of legalizing cannabis because sober cannabis-using drivers may still be a public health concern.

Other drugs

Our research has also shown that other drugs may negatively impact the ability to control a vehicle, including triazolam, diphenhydramine, alprazolam, and benzodiazepine.^2,7-10 Diphenhydramine, for example, caused more variability of lane position as well as increased lane departures, steering bandwidth, average speed, and the percentage of time spent more than 5 mph over the speed limit.⁹

Pharmacokinetics and measuring impairment

Understanding how drugs are processed in the body and their relationship to impairment is critical to providing appropriate guidance to people using the drugs as well as to policy makers as they consider the legal implications of impaired driving. Impairment from alcohol is more predictable from person to person¹¹ than impairment from cannabis, which has shown more variability in its effects on driving performance.^12-14 Blood levels of THC, for example, did not accurately represent observed levels of driving impairment—making it more difficult to predict driving behavior when under the influence of cannabis.¹⁵

Knowing that detection of drug impairment can be complicated, there is a dedicated effort to develop methods for determining whether an individual is impaired or just has drugs present in their system. Our research has shown that impaired driving can be detected based on driving data,^1,16 vision-based data,^17,18 and EEG data.¹⁹ Detection of impairment outside the context of driving is also possible as demonstrated by the relationship between EEG based tests and observed driving impairment.^20,21 These results show that a simple EEG based test focused on theta activity in the frontal brain area, the area responsible for executive function, could be developed with a limited number so sensors to detect cannabis impairment.