"From a public-health standpoint, you want people to be driving under the influence of marijuana rather than alcohol," Rees says.
He describes the BMJ report as warning of the "worst-case scenario" and refers to other driving research that shows little to no significant crash risk for some high drivers. Rees doesn't doubt that pot affects the brain, but, he says, studies show "drivers under the influence of marijuana take fewer risks. They go slower. They put more distance between them and the driver in front of them."
For years, police have hosted events in which volunteers pound down a few drinks and then take a field sobriety test. Hilarity ensues when the subjects, who are warned not to drive, stumble around and can't find their nose with their index finger. With pot, the results aren't so predictable.
A CBS affiliate in Seattle, KIRO-TV, conducted a similar test with pot users in February, allowing volunteers to drive on a closed course and give blood to measure their THC levels. Under the watch of a Sheriff's Office drug-recognition expert, three volunteers — whose pot use ranged from occasional to heavy — smoked before driving with Cascade Driving School instructor Mike Jackson.
The sheriff's deputy and driving instructor didn't notice any problems at active THC levels that were three to five times higher than Washington's new 5ng/ml limit. With increasing dosages, however, all three made driving errors that could have gotten them into a crash or pulled over by a cop.
For Jackson, the experiment "certainly raises the question of where the legislative limit should be."
In this context, Arizona's limit of zero for THC and its metabolites clearly is too low.
If you're convicted of a marijuana-DUI in Arizona, expect the usual punishment — and then some.
Besides "a boatload of fines and fees" and at least 24 hours in jail for a first offense, motorists convicted of driving with illegal drug metabolites have their licenses suspended for a full year, instead of the typical 90 days for alcohol offenders, says Valley defense attorney Michael Munoz.
A vehicle-interlock device that detects only alcohol must be installed in the offender's car, barring a waiver following a drug-and-alcohol evaluation.
The consequences are worse for a pot-DUI than for possessing pot in Arizona, the latter usually a misdemeanor offense with no jail time and a smaller fine.
Some cities, like Tempe, don't target pot-positive drivers aggressively under the zero-tolerance law, says Robert Hubbard, Tempe city prosecutor.
"I wouldn't go out on a limb and say any amount of this stuff is a slam dunk [conviction]," Hubbard says, adding that if the levels of THC or its metabolites are low, "I'm not going to prosecute."
In Phoenix, the policy calls for prosecution even on carboxy-THC, taking full advantage of the zero-tolerance law, says assistant city prosecutor Beth Barnes.
Arizona's medical-pot law, which allows qualified patients to legally possess pot, "provides no defense" for impaired drivers, Barnes says.
The 2010 law states specifically that driving under the influence of marijuana is prohibited, but it adds that patients can't be considered under the influence "solely because of the presence of metabolites . . . that appear in insufficient concentration to cause impairment."
Barnes says her office doesn't prosecute people "solely" because of the presence of metabolites. Impairment always is alleged in these cases, she explains, and they involve at least two charges: driving while impaired and driving with drug metabolites. Driving behavior, visual clues of impairment by an officer, and performance on the field test also are taken into account.
Although state law contains an exception to the metabolites provision for people with a valid prescription for the offending drug, the medical-pot law has doctors recommending marijuana for various conditions, not prescribing it.
This provides a loophole that makes it easier for prosecutors to get convictions for doctor-recommended marijuana, but not, say, doctor-prescribed Xanax or oxycodone, which may well be worse for drivers.
Admitting to having a medical-pot card during a traffic stop might even be considered one more piece of evidence in a marijuana-DUI investigation, police tell New Times.
Munoz agrees: "These medical-marijuana cards are all DUI time bombs."
Unless the Arizona Supreme Court changes the zero-tolerance law, marijuana users in this state — even motorists passing through — should keep in mind that a conviction for DUI may be one traffic stop away.