ASSESSMENT OF FUNCTIONAL IMPAIRMENT OF DRIVERS AFTER THE USE OF CANNABIS: POSSIBILITIES AND LIMITATIONS OF FIELD AND LABORATORY METHODS

Driving after cannabis use represents a significant road-safety challenge, particularly because of the difficulty in distinguishing the presence of tetrahydrocannabinol (THC) in the body from actual psychophysical impairment. Unlike alcohol, there is no simple and universally accepted relationship between THC concentration in a biological sample and the degree of a driver’s functional impairment. This paper analyses the possibilities and limitations of roadside and laboratory methods for detecting THC, as well as their importance in assessing a driver’s actual ability to operate a vehicle safely. A descriptive analytical review of relevant scientific and professional literature was conducted. Blood, urine and oral fluid testing methods were analysed, together with the characteristics of roadside screening devices used to detect psychoactive substances. Particular attention was paid to the problem of residual THC, the differences between the “impairment” and “per se” approaches, and the need to combine toxicological, behavioural and clinical indicators. The analysis shows that a positive test result, particularly in urine, does not necessarily confirm that a driver was actually impaired at the time of the traffic check. The most reliable approach involves combining behavioural observation, roadside screening, laboratory confirmation and professional assessment of the driver’s psychophysical condition. Such an approach may contribute to improving driver control and preventing road traffic accidents.