Two new studies find crashes are up in states that have legalized marijuana use.
The Insurance Institute for Highway Safety looks at emerging threats to safety.
Russ Rader said marijuana impairment has been an issue in some states where pot is legal for recreational use.
"We found that crashes were up as much as six percent in Colorado, Nevada, Oregon and Washington, compared with their neighbors that haven't legalized recreational marijuana," said Rader.
He said insurance claim data and police-reported crashes were both increasing.
"We found a similar result that police reported crashes were up just over five percent in the states that have legalized," said Rader.
He said traffic safety hasn't always been part of the debate about legalizing recreational marijuana.
He added this is worth watching because evidence shows there will be more crashes once legalized.