The report, authored by NORML’s newly appointed Deputy Director Paul Armentano, reviews more than a dozen scientific studies investigating the impact of cannabis and other controlled substances on psychomotor performance and on-road accident risk. It states: "While pot’s adverse impact on psychomotor skills is less severe than the effects of alcohol, driving under the acute influence of cannabis still may pose an elevated risk of accident in certain situations. However, because marijuana’s psychomotor impairment is subtle and short-lived, consumers can greatly reduce this risk by refraining from driving for a period of several hours following their cannabis use.

"In contrast, motorists should never be encouraged to operate a vehicle while smoking cannabis. Drivers should also be advised that engaging in the simultaneous use of both cannabis and alcohol can significantly increase their risk of accident compared to the consumption of either substance alone."

The report also states, "Past use of cannabis, as defined by the detection of inactive cannabis metabolites in the urine of drivers, is not associated with an increased accident risk." Past use of cannabis, as defined by the presence of trace levels of THC in a drivers’ blood, is also seldom associated with increased accident risk compared to drug-free drivers. By contrast, a handful of recent studies have reported a positive association between recent cannabis exposure – as defined by the presence of THC/blood concentrations above 5ng/ml – and a gradually increased risk of vehicle accident.

"In closed course and driving simulator studies, marijuana’s acute effects on psychomotor performance include minor impairments in tracking (eye movement control) and reaction time, as well as variation in lateral positioning, headway, and speed," the report states. "[However,] these variations in driving behavior are noticeably less consistent or pronounced than the impairments exhibited by subjects under the influence of alcohol. Also, unlike subjects impaired by alcohol, individuals under the influence of cannabis tend to be aware of their impairment and try to compensate for it accordingly, either by driving more cautiously or by expressing an unwillingness to drive altogether."

NORML’s report calls for the creation of a nationwide public health campaign to educate younger drivers of the potential risks posed by drugged driving. The report also calls for the development of roadside, cannabis-sensitive technology to better assist law enforcement in identifying drivers who may be under the influence of pot.

"The development of such technology would also increase public support for the taxation and regulation of cannabis by helping to assuage concerns that liberalizing marijuana policies could potentially lead to an increase in incidences of drugged driving," the report concludes. "Such concerns are a significant impediment to the enactment of marijuana law reform, and must be sufficiently addressed before a majority of the public will embrace any public policy that proposes regulating adult cannabis use like alcohol."

Full text of the report, "Cannabis and Driving: A Scientific and Rational Review," is available online at: http://www.norml.org/index.cfm?Group_ID=7459.