Despite all the handwringing about driving under the influence of marijuana in the brave new world of legalized recreational pot, little will change in terms of motorist behaviors, arrests, or prosecutions.
As a longtime criminal defense attorney and former prosecutor who has handled thousands of DUI cases, I note that there is a substantial difference in DUI alcohol and DUI marijuana. Marijuana simply does not affect driving as negatively as alcohol. While most DUI alcohol arrests are made because of police stops based on obviously bad driving, most DUI MJ arrests take place after the police have made a stop for some other minor infraction (taillight, registration violation, routine traffic matter), and then smell marijuana in the car.
Despite legalization, incidents of DUI MJ will not significantly increase. Let’s not kid ourselves, people who choose to smoke marijuana have not been much deterred by the fact that it was illegal. Moreover, due to legalized medical marijuana being readily available, there has been a reliable supply of high quality, THC laden, pot available to virtually anyone who wanted it. Legalization is unlikely to significantly increase the number of people who smoke pot, nor for that matter, likely to increase the number who drive while under its influence.
For a prosecutor to win a DUI case, she must prove to a jury that the defendant’s ability to drive was significantly impaired by use of a substance or some combination of substances, beyond a reasonable doubt. Modern legislation deems that anyone with a .08 blood alcohol is driving illegally, whether or not their driving is actually impaired. The .08 level was determined after much scientific research and testing. For a variety of reasons, no such testing has been done on marijuana levels and driving performance, therefore, prosecutors have no reliable blood/marijuana tool at their disposal. Therefore, a DUI MJ case would have to be made on circumstantial evidence: bad driving, accident, smell of pot in the car, poor Field Sobriety Tests, admissions of the defendant, etc. This is not an impossible prosecutorial standard, but it is far more difficult than simply proving .08 or higher. Add that to generally friendly to marijuana use Bay Area juries and it is not hard to see the uphill battle a DUI MJ prosecutor faces.
The reality is that legalization will cause only a marginal increase in marijuana use, a minor increase in DUI MJ, little change in DUI MJ detection and enforcement by police, and not much change in prosecutorial attitudes toward DUI MJ cases.