Overall the evidence suggests that cannabis impairs driving ability and increases a driver’s risk of being involved in a car crash.

A number of studies have shown that cannabis affects memory, psychomotor abilities, reaction times and these effects remain long after the ‘high’ has passed.
The perception that drugs do not significantly impair driving capability would appear to be common among drug users. In fact they often perceive that their driving skills are unaffected by drugs and in some cases makes them better drivers.

Many regular drug-drivers believe compensatory strategies can reduce the risks when drug-driving. Studies with cannabis users have found that it is safe to drive following cannabis use and that it does not increase collision risk.

Drug- drivers perceive little risk of apprehension, perceive themselves to be better drives while under the influence of some drugs, perceive low risk of collision compared with alcohol, overestimate their ability to compensate for impairment and demonstrate little knowledge of the effects of driving under the influence of different drugs.