How Will Prop 64 Impact DUI’s In California?


Now that Prop 64 has passed, will we see more drivers under the influence on California roads? Maybe. But as I discussed in previous posts, unlike alcohol, there is no definitive way to test for the immediate presence of THC (the chemical in marijuana and marijuana derivatives that makes a person “high”) in a person’s system. Furthermore, while the DUI laws make it illegal to drive under the influence of marijuana, whether a driver is under the influence is a subjective assessment made by the detaining officer and unless the car is reeking of pot, the evidence may be difficult to prove in court. While science and the legislature are working on better testing and specific statutory limits, the state is currently in the predicament where recreational use of marijuana is legal, much like alcohol use, but the laws controlling driving under the influence of marijuana are ambiguous.

The critics of Prop 64 pointed out that the proposition does not include a DUI standard for marijuana. Colorado has, for example, included in their statute a driving under the influence of marijuana threshold of 5 nanograms of THC. Still, as I previously discussed, scientists have not come up with a device as accurate as a roadside breathalyzer and that is problematic. Colorado may lead the way though as the police there are now testing five types of oral fluid testers that allow the police to check a driver’s saliva for THC at the time of the traffic stop. And even though there is no threshold standard for marijuana in a driver’s system (similar to the .08% BAC in the DUI laws) at the present time, that does not mean the Legislature cannot enact a law with such a standard—and they most certainly will.

California expects to gain $1 billion annually in tax revenues generated by the sale of recreation marijuana. In an effort to address driving under the influence of this now legal substance, 20%, of that revenue, which equates to an expected $200 million per year, will be designated to train police on enforcing driving under the influence of marijuana laws and to educate drivers about the dangers of driving under the influence of marijuana.

Evidence coming out of states that have already legalized marijuana indicates that there is an uptick in drivers on the road who are under the influence of marijuana. And there are statistics from law enforcement suggesting that fatal collisions involving drivers under the influence of marijuana in those states has as much as doubled. Of course, there are other statistics that suggest this is not true, most notably the study I discussed, which was conducted by the National Highway Traffic Safety Administration.

It will take years for California and other states to sort out the societal impacts of legal marijuana and the effects it might have on driver safety. But drivers must be cautioned that even though they can now legally get high on pot, they can’t drive high. Without valid scientific tests available, even the smell of pot on a driver’s person might be enough to convince the DMV (in an Administrative Per Se Hearing) and the court that the driver was under the influence of marijuana. Of course, edible marijuana, which is often the marijuana use of choice, does not leave that tell-tale smell. Until a valid roadside test is developed for testing drivers for marijuana in their system, driving under the influence of marijuana is and will continue to be difficult for the state to prove.

William Weinberg has almost 25 years experience defending DUI arrests. If you have been arrested for any driving under the influence offense of have any questions concerning driving under the influence, you may contact Mr. Weinberg at his Irvine office at (949)474-8008 or at

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