The effects of cannabis on driving performance were similar to those of low blood alcohol concentrations.
Cannabis use on its own reduces lateral control of the vehicle (the ability to stay in the lane) even though drivers under the influence of cannabis slow their driving speed, possibly in an attempt to compensate for their impaired state.
In contrast, alcohol use on its increases driving speed, which may indicate that drivers under the influence of alcohol lack awareness of their impaired state.
Alcohol also affects a greater number of driving performance indicators relative to cannabis, including increased crashes, lateral position variability, lane excursions, speed, and speed variability, as well as reduced hazard response time.
The combination of both drugs generally impairs the ability to maintain lane position more than either substance taken on its own. The study found no evidence that the two drugs counteract each other on speed.
Source: Eurekalert
