This seems a little weird, but then I’m not a smoker. State police and public safety officials in Massachusetts — and automobile insurance representatives nationally — are urging drivers to remain alert and extra careful today, April 20, especially in the late afternoon.

It sounds like an urban myth. But a recent study by the American Medical Association on driving and the growing use of marijuana found a 12 percent increase in automobile accidents on April 20 (4/20), sometimes known as National Weed Day, and especially after 4:20 in the afternoon.

In Boston Thursday, State Police Col. Kerry Gilpin and Secretary of Public Safety and Security Dan Bennett warned that both drinking and marijuana use affect reaction times and cognitive functions in driving and the effects are magnified by combined use of both substances.

“Driver responsibility plays a huge role in keeping our roads safe,” said Bennett, “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.”

Gilpin added: “Our Troopers will be stopping any motorists who are driving dangerously and putting others at risk.”

According to legend, association of 4/20 with marijuana use began back in the 1970’s at a California high school where students would gather outdoors to smoke marijuana after classes at 4:20.

The website Business Insurance noted this week:

Despite evidence that U.S. traffic deaths increase dramatically every April 20, otherwise known as National Weed Day, a majority of Americans don’t think there’s any danger on the roads, the Property Casualty Insurers Association of America said Wednesday.

Chicago-based PCI said in a statement that an online survey of over 1,000 adults conducted April 5-12 found that more than 68% of respondents see no difference in road safety on April 20 than on the same day one week before or one week after.

Impaired driving under the influence of marijuana has become an increasing concern. Since 2012 nine states, mostly in the West, and the District of Columbia have legalized recreational marijuana use. Twenty-nine states and D.C. have legal marijuana prescriptions.

So, clearly, no matter where you’re driving today, it’s probably best if you get home by 4:16 p.m. or 4:18 at the latest.