Jacob Sullum does tremendous work over at Reason. Recently, he wrote about a study by the National Highway Traffic Safety Administration ("NHTSA") that analyzed the impact of marijuana on drivers and whether it tended to increase the likelihood that a driver would crash. The bottom line is that after accounting for demographic factors (age and gender, mostly), the NHTSA study could not isolate a scientifically valid relationship between using marijuana and an increased probability of getting into an accident.
That is really big news.
Here is the money shot on THC from the NHTSA study:
"Table 4 examines the odds ratios for the same categories and classes of drugs, adjusted for the demographic variables of age, gender, and race/ethnicity. This analysis shows that the significant increased risk of crash involvement associated with THC and illegal drugs shown in Table 3 is not found after adjusting for these demographic variables. This finding suggests that these demographic variables may have co-varied with drug use and accounted for most of the increased crash risk. For example, if the THC-positive drivers were predominantly young males, their apparent crash risk may have been related to age and gender rather than use of THC." (Emphasis added.)
Table 4 is shown on page 5 of the above-referenced study. The blurb I cited above comes from the lower right and corner of page 4.
It goes without saying that NHTSA (the "National Highway Traffic Safety Administration") is hardly a front organization shilling for the DUI defense/criminal defense bar. To the contrary, NHTSA is extremely interested in combating risk factors for highway death, disfigurement, and injury. They did their best to bury this study and the finding, and admitted the true nature of their findings only as a result of some skeptical, courageous, and scientifically literate members of Congress dragging it out of them in a hearing.
I am as concerned about drugged driving as the rest of society -- I want to be safe. I want my kids to be safe. I want all of you to be safe. But I also want law and policy to be based on real science so that laws can be written and enforced in a way that criminalizes only conduct that is actually a safety threat. What the current "drugged driving" law in Pennsylvania does with marijuana is to criminalize being a young man (which generally means being a worse driver). It does not criminalize any additional risk from using marijuana, at least according to this NHTSA study.
If we are collectively going to criminalize actually dangerous drugged driving, fine. Let's be very careful that we are not actually criminalizing things, as in this case, such as being an inexperienced, young, male driver.