In their review of driving simulator studies, Kelly and colleagues17 concluded that there is evidence of dose-dependent impairments in cannabis-affected individuals’ ability to control a vehicle in the areas of steering, headway control, speed variability, car following, reaction time and lane positioning. They noted, however, that the levels of impairment detected in simulator studies did not appear to replicate those found in laboratory studies, and speculated that this may be due to the cannabis-affected participants consciously compensating for their impairments. Nonetheless, it should be acknowledged that “even in those who learn to compensate for a drug’s impairing effects, substantial impairment in performance can still be observed under conditions of general task performance (i.e. when no contingencies are present to maintain compensated performance.