Strengths and limitations of two cannabis-impaired driving detection methods: a review of the literature.
Background: Recent cannabis use is associated with an approximate two-fold increase in automobile crash risk, but detecting cannabis-impaired driving remains a challenge.Objectives and Methods: In this perspective, the pros and cons of two types of assessments arising from those used to detect alcohol-impaired driving are discussed in the context of cannabis-impaired driving.Results: Some laws rely on tests to detect whether blood or breath levels exceed a legally defined (per se) threshold. These laws rely on clear and consistent relationships across individuals between detectable drug concentrations and the amount consumed, crash risk, or degree of driver impairment. However, unlike alcohol, there is poor correspondence between detected levels of the primary active constituent of cannabis or its metabolites and the amount consumed or its behavioral effects. Field sobriety tests assess impairment on functional tests calibrated to reflect actual driving-impairment and validated to predict traffic safety risk. However, functional tests for cannabis-impaired driving have not been developed or validated, and the degree of impairment resulting from recent cannabis use is difficult to distinguish from other conditions such as advancing age or use of certain medications.Conclusions: Although standard field sobriety tests have advantages over per se tests for cannabis-impaired driving, limitations of both leave cannabis users and law enforcement officials little guidance in assessing an individual's driving fitness after recent cannabis use. General strategies for detecting and preventing impaired driving regardless of the cause would be preferable to establishing specific methods for every situation or substance that could impair driving.