Authors reported that the use of cannabis, absent the simultaneous use of other drugs or alcohol, creates “only a fraction of the risks associated with driving at the legal 0.08 BAC threshold, let alone the much higher risks associated with higher levels of alcohol.” By contrast, they report that “the simultaneous use of alcohol and cannabis is linked to higher levels of driver impairment than either alone” – a finding that is consistent with much of the available literature.
They conclude, “The maximum risk for cannabis intoxication alone, unmixed with alcohol or other drugs, appears to be more comparable to risks such as talking on a hands-free cellphone (legal in all states) than to driving with a BAC above 0.08.” As a result, they suggest that as a matter of policy, “stoned driving alone (not involving alcohol or other drugs), should be treated as a traffic infraction rather than as a crime, unless aggravated by recklessness, aggressiveness, or high speed.”
In virtually all instances, cannabis-influenced driving is classified as a criminal rather than an administrative offense.
Investigators also argued against the imposition of per se limits which criminalize the act of operating a vehicle with trace levels of either THC or THC metabolites in one’s blood or urine. They determined: “Blood THC is not a good proxy either for recency of use or for impairment, and the dose-effect curve for fatality risk remains a matter of sharp controversy. … Moreover, the lipid-solubility of THC means that a frequent cannabis user will always have measurable THC in his or her blood, even when that person has not used recently and is neither subjectively intoxicated nor objectively impaired.”
The US National Highway Traffic Safety Administration (NHTSA) and the American Automobile Association(AAA) take a similar stance against the use of blood/THC concentrations as per se evidence of psychomotor impairment. NORML has long articulated similar opposition, stating, “Per se limits and zero tolerant per se thresholds … are not based upon scientific evidence or consensus. … [T]he enforcement of these strict liability standards risks inappropriately convicting unimpaired subjects of traffic safety violations, including those persons who are consuming cannabis legally in accordance with other state statutes.”