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Abstract
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How is driving performance measured?
Driving is a complex and demanding task that involves a wide range of cognitive, perceptual, and motor functions. The most common measure of driving performance is the standard deviation of lateral position (SDLP), a measure of lane weaving, swerving, and overcorrecting. It is very sensitive to alcohol and drug effects. The change in SDLP associated with a blood alcohol concentration (BAC) of .05 is widely used as the benchmark for clinically relevant driving impairment1 as this is the legal driving limit in many jurisdictions. Other common measures include reaction time, speed, and headway (the distance a driver leaves between their vehicle and the vehicle ahead).
Since individuals have a different baseline level of driving performance, experimental studies generally examine how driving performance changes under different conditions. Researchers do this by comparing a driver's normal level of performance (e.g., after receiving a placebo or before being given alcohol or cannabis) to their performance after being given a particular dose of alcohol or cannabis or being deprived of sleep. The most realistic way to assess driving performance is by conducting an on-road study in which participants drive while supervised under real-world conditions. However, these designs are not often used because of the ethical and logistical challenges that they entail. Driving simulators are commonly used instead. In addition to their practicality, a key advantage of using a driving simulator is that investigators can control every aspect of the driving environment, including weather and road conditions, vehicle dynamics, and other vehicle behaviours.2 This makes it possible to simulate scenarios and conditions that would be impossible to control, and thereby ethically test, in the real world.
How much does cannabis impair driving?
Cannabis impairs driving, although the degree of impairment it produces varies substantially depending on the dose and the individual.
A series of on-road studies conducted in the Netherlands in 2000 established that smoked cannabis (100 and 200 μg/kg THC) significantly increases a driver's SDLP.3 This finding has been confirmed by most studies since, including a study which used ... the highly advanced driving simulator at the University of Iowa.4 In a very recent on-road study5, participants vaporized several types of cannabis that contained different ratios of tetrahydrocannabinol (THC) to cannabidiol (CBD). Regardless of the ...
How long after using cannabis are drivers safe to drive?
If a driver tests positive for THC, does that mean they are impaired?
What are the limitations of experimental studies of cannabis and driving?
Keywords: cannabis impaired driving |