The imposition of so-called per se drugged driving laws, which create new traffic safety violations for drivers who operate a vehicle with the presence of trace amounts of certain controlled substances and/or their inert metabolites (byproducts) in their blood or urine, do not reduce incidences of traffic safety deaths.

That’s the conclusion of a just-published study by economists at the University of Colorado, Denver and Montana State University. The study is available from the Institute for the Study of Labor (IZA) in Germany as a Discussion Paper.

Since 1990, 11 states have passed so-called zero-tolerant per se drugged driving laws which make it illegal for one to drive with detectable levels of a controlled substance in his or her system. Five additional states have passed similar laws specifying non-zero limits for controlled substances or their metabolites. Fourteen (Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Nevada, Ohio, Pennsylvania, Rhode Island, Utah, Washington, and Wisconsin) of these sixteen states impose these strict liability per se standards for cannabis. Recently, the White House Office of National Drug Control has recommended zero tolerant per se drug standards for all US states.

Using state-level data from the Fatality Analysis Reporting System (FARS) for the period 1990-2010, authors examined the relationship between the adoption of controlled substance per se thresholds and overall incidences of traffic fatalities. They found that the relationship is statistically indistinguishable from zero and concluded that there is no evidence that these limits reduced traffic deaths.

Authors reported: “Despite the fact that these laws have been touted by politicians and academics as an effective strategy for making our roadways safer, we find no evidence that they reduce traffic fatalities. … [W]e cannot determine why per se drugged driving laws do not work, and leave this issue to future researchers. However, our results clearly indicate that, as currently implemented, laws that make it illegal to drive with detectable levels of a controlled substance in the system have little to no effect on traffic fatalities.”

In November, Washington state voters approved Initiative 502, which legalizes the private use and retail sale of cannabis to adults, but also imposes a 5ng/ml THC/blood per se limit for drivers over the age of 21. In Colorado, where voters on Election Day similarly legalized cannabis, Democrat Gov. John Hickenlooper and Republican Senator Steven King are calling for the passage of nearly identical per se cannabis legislation.

NORML has consistently opposed the imposition of stand-alone per se limits for cannabinoids, arguing that the presence of THC in blood, particularly at lower levels, is an inconsistent predictor of behavioral impairment, particularly in more frequent consumers who may potentially test positive for trace, residual THC levels in their blood for periods of time exceeding any period of acute impairment.

Operation of a motor vehicle while under the influence of cannabis is already a criminal offense in all 50 states. However, in order for one to gain a criminal conviction under most state DUI laws, prosecutors must prove that a motorist recently ingested cannabis and that doing so prohibited him or her from driving safely.

Full text of the study, “Per Se Drugged Driving Laws and Traffic Fatalities,” is available online here. A separate paper previously published by the same authors reported that the passage of statewide medical marijuana laws is associated with decreased incidences of traffic fatalities.

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