In a report issued last week, a legislative committee charged with considering the implications of marijuana legalization in Massachusetts says "there is no well-accepted standard for determining driver impairment from marijuana intoxication." The report's authors nevertheless recommend "establishing a legal limit for THC blood concentration that would support at least a permissible inference standard in court." That is the approach taken by Colorado, where it has proven more favorable to defendants than the per se rule in Washington, under which any driver who exceeds a specified THC blood level is automatically deemed impaired. But Colorado's approach is still scientifically unsound, making it easier to convict innocent people than the current law in Massachusetts.
It seems strange that the legislators who wrote the Massachusetts report, after conceding that there is no scientific basis for tying the legal definition of impairment to a particular THC level, would recommend tying the legal definition of impairment to a particular THC level. They do not say what the level should be, possibly because that would only serve to highlight how arbitrary such cutoffs are. "Whereas the impairment effects for various concentration levels of alcohol in the blood or breath are well understood," the National Highway Traffic Safety Administration notes, "there is little evidence available to link concentrations of other drugs to driver performance." Hence "specific drug concentration levels cannot be reliably equated with a specific degree of driver impairment."
That fact makes life more difficult for cops and prosecutors, which explains the appeal of a per se rule. But the same uncertainty makes a per se rule clearly unjust. The "permissible inference" approach aims to split the difference between a per se rule and current Massachusetts law, which requires the government to show a driver consumed enough of a drug to "reduce his ability to operate a motor vehicle safely by diminishing his alertness, judgment, and ability to respond promptly." Blood test results can be presented as evidence, but they are not conclusive. Colorado, by contrast, allows (but does not require) a DUI conviction based on nothing more than blood test results.
The THC cutoff in Colorado is the same as in Washington: five nanograms per milliliter. But while exceeding that level in Washington automatically leads to conviction, Colorado defendants can try to persuade jurors that they were not in fact impaired, and that distinction has proven decisive in many cases.
Consider Ralph Banks, who was pulled over in Lakewood, a Denver suburb, last March because of a broken headlight. The officer who stopped Banks noticed that he smelled of marijuana—which was not surprising, since he grows the stuff for Medicine Man, a state-licensed pot store in Denver—and asked him to perform roadside sobriety tests. The officer reported that Banks "failed to perform at a satisfactory level." He was arrested for DUI, and a blood test put his THC level at 7.9 nanograms per milliliter, well above the cutoff. He was nevertheless acquitted earlier this month.
Rob Corry, Banks' lawyer, says a physician who testified for the defense and the arresting officer, who is considered a "drug recognition expert," agreed that "marijuana affects every person differently." Although the officer said he was convinced Banks was intoxicated, there was no evidence of careless driving, and Corry was able to cast doubt on the validity of the roadside tests. "We established that the roadsides are generally designed for alcohol detection, which was not a factor in this case," Corry says. "Furthermore, performance on them is a subjective analysis. Much of it is touchy-feely garbage. Glassy eyes, nervousness, estimating 30 seconds with eyes closed and head back, etc. Police in Colorado (to their detriment) never videotape roadsides, so juries are left with analyzing the subjective memories of police officers' opinions about performance rather than objective evidence."
Banks did not testify, but he told the officer he had not smoked marijuana in four or five days. Corry says Banks had used a cannabis-infused muscle rub earlier that day. That could help account for for his THC level, which in any event was not especially high for regular cannabis consumers, even when they are not impaired. "The commonsense suggestion was made that frequent, experienced marijuana consumers understand how marijuana will impact them, better than novices," Corry says. It took the jurors just half an hour to acquit Banks.
"We have prevailed in numerous marijuana DUI cases around the state, both before and after the five-nanogram permissive inference standard was superimposed by the legislature," Corry says. "The [rule] lacks much validity, and some juries are smart enough to see through it." He says it is "challenging to overcome but not impossible."
While Colorado's approach is better than Washington's, Corry says, the pre-legalization standard, which was similar to the current law in Massachusetts, was preferable to both:
I am not optimistic that innocent people will not be wrongly convicted under this inference. Some juries (and all police and prosecutors) latch onto the five-nanogram number as if it is the same as the 0.8 [percent] blood alcohol standard….The previous system, though imperfect, worked better in sorting out the guilty from the innocent. Prosecutors had to come in with actual evidence of impairment. Other drugs that can cause impairment (such as prescription opiates) have no numerical standards, but it is still illegal to operate a motor vehicle while impaired by them. The difference is that the prosecution must actually prove their case through real evidence to prevail. Every person is different. Levels of impairment vary depending on many factors, especially a person's level of knowledge and experience with the particular drug.
Washington's per se rule was included in that state's legalization initiative as way of reassuring voters that legalization would be accompanied by efforts to prevent stoned driving. Colorado's initiative, by contrast, left the DUI law unchanged, and it was state legislators who enacted the current rule. In Massachusetts, the legalization initiative that is expected to be on the ballot in November likewise does not change the state's definition of DUI (known there as OUI, for "operating under the influence"). The Special Senate Committee on Marijuana, which issued last week's report, is urging Massachusetts legislators to follow Colorado's example. It says "methods and procedures for determining driver impairment due to marijuana, including establishing a legal limit for THC blood concentration that would support at least a permissible inference standard in court," should be "adopted by statute and in place before any effective date of marijuana legalization." If the THC limit is supposed to be scientifically sound, that goal would delay legalization indefinitely.