The National Highway Traffic Safety Administration just finished the largest-ever study documenting the risks associated with drunk or drugged driving. While the results on alcohol and driving weren’t entirely surprising, there was an unexpected result in terms of marijuana’s role in traffic accidents.

For the Drug and Alcohol Crash Risk study, researchers interviewed and tested some 9,000 drivers in Virginia Beach, Virginia, over the course of 20 months. More than 3,000 of those drivers had been in car accidents; the others constituted a control group of drivers who had not. The non-crash drivers were chosen because they happened to be driving through the same area at the same time of the day, on the same day of the week, and in the same direction of traffic as those who had been in crashes. All of the drivers were tested for alcohol and drugs, although marijuana was the only drug used commonly enough for the findings to be considered statistically significant.

The more drunk the driver, the greater the risk of a crash

As you might expect, the study found that drivers with a blood alcohol content of 0.08 – the legal limit here in South Carolina and throughout the country – were indeed more likely to get into crashes. Adjusting for age and gender, which also affect car accident risk, it turned out that 0.08 drivers were about four times more likely to be involved in traffic accidents than sober drivers. Drivers with a blood alcohol content of 0.15-percent were 12 times more likely.

No statistically significant difference between sober and marijuana-using drivers

According to NHTSA, it was certainly the case that marijuana users were overrepresented in the group of drivers who had been in crashes. On its face, that fact seems to indicate that driving under the influence of THC, the active chemical in marijuana, increases your risk of being in an accident. However, when the raw numbers were adjusted for age, gender, and whether the driver was also under the influence of alcohol, that conclusion came into question. Overall, the study found no statistical evidence that testing positive for THC itself increased crash risk.

That said, if you’ve been hit by a drunk or drugged driver, you won’t be satisfied with statistics. You can certainly use evidence of the other driver’s marijuana use to prove that driver was at fault.