This paper describes the methodology of a programme, sponsored by the US National Highway Traffic Safety Administration (NHTSA), to investigate various aspects of marijuana's effects on driving safety. It was presented too early to give the results of its studies. The objectives were to: (1) measure the dose-response relationship between marijuana (THC) and objectively and subjectively measured aspects of real-world driving; (2) determine if driving performance impairment could be correlated with plasma concentrations of marijuana as a metabolite. Various driving tasks were tested, including: (1) maintaining a constant speed and lateral position during uninterrupted road travel; (2) following a leading car with varying speed on a road; and (3) city driving. All the participants were current users of cannabis and had a driving licence. They indicated that they had driven at least once during the past year within an hour of smoking cannabis. Their blood and urine were analysed during tests after they had smoked THC. After a pilot study to select THC doses, the following driving studies were conducted: (1) on a closed section of a public road; (2) on a primary road in the presence of other traffic; (3) in high-density urban traffic.
Abstract