The use of cannabis is not without potential risk (“Maine study group recommends THC blood level-limit for marijuana-using drivers,” Dec. 15). But such risks need to be placed in proper context.

A recent National Highway Transportation Safety Administration study assessed whether those who are THC-positive possess an elevated risk of motor vehicle accident compared to those who test negative. They found no statistically significant risk after adjusting for age and gender (OR=1.05).

By contrast, alcohol-positive drivers (within legal limits) possessed a fourfold risk of accident. Driving with two or more passengers in the car increases one’s risk of traffic accident more than twofold.

Nevertheless, the use of cannabis prior to driving ought to be discouraged, and better efforts ought to be made to identify drivers who may be under its influence. These include greater use of drug recognition evaluators, the use of modified roadside field sobriety tests and the provisional use of roadside cannabis-sensitive detection technology, such as saliva test or breath test.

But these efforts should not include the imposition of arbitrary and unscientific per se laws for THC in blood. As acknowledged by the National Highway Transportation Safety Administration: “It is difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects. … It is inadvisable to try and predict effects based on blood THC concentrations alone.”

As states like Maine consider amending their cannabis consumption laws, lawmakers ought not to amend traffic safety laws in a manner that relies solely on the presence of THC or its metabolites as determinants of guilt in a court of law.

Otherwise, the imposition of traffic safety laws may inadvertently become a criminal mechanism to punish those who have engaged in legally protected behavior and who have not posed any actionable traffic safety threat.

Paul Armentano

deputy director, National Organization for the Reform of Marijuana Laws

Washington, D.C.