When Oregon legalized recreational marijuana, some state officials worried car crashes could increase.

A new study indicates that didn’t happen, though more research is needed.

Back in 2004, when Oregon only had medical and black-market marijuana, there were 13 traffic fatalities involving the drug. In 2015, with recreational cannabis on store shelves across the state, 16 people died in marijuana-related traffic accidents.

“To this point, as a result of legalization, we haven’t seen a large spike or epidemic of … THC driving,” said T.J. Sheehy, an Oregon Liquor Control Commission official who authored the study 

Unlike Colorado and Washington, Oregon doesn’t have a marijuana blood concentration limit for drivers. Instead, if a police officer thinks a driver is high in Oregon they’ll call in a “drug recognition expert” who will ask questions and take a blood or urine sample.

Oregon leaders decided against having a blood limit because the active ingredient in marijuana, THC, is fat soluble. That means it stays in the body for weeks. Alcohol, on the other hand, can be metabolized within a matter of hours.

Thus, a blood count is not a great way to tell if a person has used marijuana recently. And that can cause a problem for lawyers trying to convict.

The study found that teenagers are more willing to drive under the influence of marijuana than alcohol. The report recommends a public education campaign.