BOSTON (CBS) – The state is asking drivers to be on high alert on Friday, as research shows the April 20 date brings an increase in the number of drivers under the influence of marijuana.

A recent study by the Journal of the American Medical Association found a 12 percent increase in deadly crashes on April 20 after 4:20 p.m.

The number 420 has become associated with marijuana use. The reason why traces back to a California high school in the 1970s.

As the story goes, students would meet at 4:20 p.m. each day on campus to smoke marijuana. The group developed a relationship with the Grateful Dead, and the band helped the term become more widespread.

On Thursday, one day ahead of 4/20, State Police Col. Kerry Gilpin and Secretary of Public Safety and Security Dan Bennett warned drivers not to get behind the wheel if they are under the influence.

“Driving while impaired is both dangerous and illegal,” said Secretary of Public Safety and Security Dan Bennett. “Driver responsibility plays a huge role in keeping our roads safe – whether we’re talking about marijuana or alcohol – and we want to remind drivers not to take the wheel if they are impaired in any way.”

The Centers for Disease Control and Prevention said marijuana can lead to slowed driver reaction time, impaired decision-making, reduced coordination and distorted perception.

“Drivers who are impaired are a danger to everyone on the road and to themselves,” said Gilpin. “Our Troopers will be stopping any motorists who are driving dangerously and putting others at risk.”