When a THC Driving Simulator Matches the Road—and When It Does Not
A driving simulator can reproduce an oral-THC effect on lane weaving without reproducing its effect on following another vehicle. A controlled comparison found precisely that distinction. “Validated simulator” is therefore too broad a description unless the particular driving measure is identified.
Comparing the same treatments in two settings
Veldstra and colleagues studied 24 experienced drivers receiving placebo or oral dronabinol at 10 mg and 20 mg. Participants completed both simulated and on-road driving assessments. The researchers examined standard deviation of lateral position, a measure of weaving within a lane, and car-following performance.
This design provided a stronger test of simulator validity than comparing unrelated studies with different populations or doses. It asked whether the effects of a treatment were similar across the two testing environments, rather than merely whether drivers could perform similar-looking tasks.
Lane control and car following gave different answers
The treatment effects on lane weaving were broadly comparable. However, greater variability in simulator measurements made the lower-dose effect less clearly detectable there. Agreement in the direction of an effect does not guarantee equal sensitivity to detect it.
The car-following results did not show comparable treatment effects across settings. A following task requires responses to another vehicle’s changing speed, so evidence supporting one measure of lateral control cannot simply be carried over to that different behavior.
Why testing order matters
The on-road assessment preceded the simulator assessment. The order was not counterbalanced. Consequently, differences between settings could also reflect elapsed time after dosing, practice or fatigue. The participants’ cannabis-use histories also varied, limiting assumptions about how the same dose would affect every driver.
The study supports a specific application of simulated lane-control research; it does not validate every simulator, task or cannabis product. Oral dronabinol results also require care when applied to inhaled cannabis, because administration route changes the time course. Our discussion of edible and vaporized cannabis timing explains why that distinction matters when interpreting a test conducted after an alleged driving event.
Primary research
Comparing treatment effects of oral THC on simulated and on-the-road driving performance: testing the validity of driving simulator drug research. DOI: 10.1007/s00213-015-3927-9.
