When a driver is stopped and believed to be driving with alcohol in their system they can take a test which will register if they are above the legal limit of 0.08 blood-alcohol content.
With drugs, it is more complex. There is no legal limit threshold for drugged driving in California.
As a result police are changing their training and testing, important details drivers need to be aware of before hitting the road. The number of known drug-positive fatally-injured drivers increased from 3,994 in 2006 to 5,365 in 2016, a 34 percent jump, according to data from the National Highway Traffic Safety Administration.
"It's epidemic," said Glendale Sgt. Craig Tweedy. "It's off the charts and with an increase in drugged driving deaths nationwide."
The complexity on these cases is huge, he said.
"If they're impaired then they go to jail," said Glendale Officer Brian Duncan.
He is one of a handful of officers who have been trained as Drug Recognition Experts.
Glendale and several other local agencies have hired a private company, called vital medical services. They use nurses to draw blood when an officer suspects a driver is impaired. A nurse from the company can respond to the scene.
"When we stop the driver we want that level of intoxication," Tweedy said.
Duncan has been a drug recognition expert officer for 18 years.
Duncan's training and experience allow him to testify in court when he believes someone is too high to drive. During a recent traffic stop, he pulled a driver over for speeding and not wearing a seatbelt.
"I could smell the weed inside the car," he said.
After a series of questions and a roadside evaluation, a nurse was called, blood was drawn, and the driver was arrested.
"I formed the opinion that he was operating a motor vehicle upon a roadway while impaired under the influence of cannabis," Duncan said.
Still, even those behind the testing say the legal system has a lot of catching up to do.
"What we're seeing in marijuana today and in regards to the enforcement of it is what alcohol was to law enforcement in the 70s," Ghazalpour said. "It's the unknown."
DUI defense attorney Phillipe Placentia questions the system.
"When it comes to drugs, it's all opinion," he said. "In my opinion more innocent people have been convicted when it comes to alcohol or drug DUI cases than any other crime in the United States."
Plancentia is not saying the officers are doing anything wrong, or making bad arrests.
Many departments don't take the extra step of having multiple DRE officers, or curbside blood draws like Glendale.
Placentia says the problem is perception. He says there is no scientific way to measure impairment.
"Everybody seems like it's OK to smoke marijuana and operate a motor vehicle and it's not," Duncan said.