SAN DIEGO — It's legal for Californians to smoke marijuana now, but how soon after lighting up is it safe to drive? University of California, San Diego researchers are trying to figure that out to help both users and law enforcement.

UCSD's Center for Medicinal Cannabis Research (CMCR) teamed up with the California Highway Patrol for the study, which was authorized by the California Legislature.

After an initial visit, study participants smoke cannabis and then undergo a driving simulation. The marijuana joints have different doses, from no THC to high THC.

"If you smoked this morning are you impaired throughout the day? Are you impaired for a couple of hours? Or are you not impaired? We're trying to answer that," said Tom Marcotte, Co-Director of the CMCR.

Marcotte says determining if someone is impaired from marijuana is more complicated than alcohol. A habitual cannabis user can have THC in their system and not be impaired.

Participants complete driving simulations, field sobriety tests, iPad-based performance assessments, and bodily fluid draws.

With the iPad tests, researchers are testing memory, attention, and motor control. What they learn in the study could help identify new field sobriety tests for law enforcement.

With 180 participants, Marcotte says their study is the largest of its kind so far.

Anyone interested in participating in the paid study can apply here.

Researchers are still looking for about 80 participants, and they must have experience using cannabis. The application states that participants will be reimbursed for their time.