It’ll be interesting to watch the legislatures and courts wrestle with the problems arising out of the evolving legalization of marijuana and whether and how much impairment it creates in its users and how that relates to driving safely and DUI laws. Any effort to defend existing or pass new legislation penalizing strictly THC metabolite, which has no pharmacological effect, are doomed to fail. That leaves the options essentially to a subjective evaluation of agility performance and driving pattern or a combination of level of THC and agility. Well grounded and well run studies have resulted in conflicting results on simple and differing levels of THC and their relative effect on driving safety. Without reliable agility tests, reasonable doubt will remain as a potentially solid defense. Those divergent studies can and will continue to provide valid arguments to any attempts to establish constitutionally defensible presumptive levels of THC. A rebuttable presumption based statute may survive challenge with appropriate guidelines and language.
Legislatures and courts would do well to pay close attention to these studies and the ongoing results of the laws in both Washington and Colorado, as well as the many states with medical marijuana and semi openly lawful marijuana laws. And any good lawyer should understand and apply the potential defenses to these charges.