We all know that recreational use of marijuana in Massachusetts is now legal, with pot shops expected to pop up all summer.

But today is April 20, or "420", and at 4:20 PM today, people are gonna "celebrate".

What we may not know, is that fatal car crashes increase on 4/20 after 4:20, according Massachusetts Public Safety officials.

Driving while impaired is both dangerous and illegal. 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. -Gov. Baker's Public Safety Chief, Dan Bennett.

Studies show that there is a 12 percent increase in fatal car crashes on April 20 after 4:20 PM, and that troopers will be on the lookout for people driving dangerously.

The Centers for Disease Control and Prevention say marijuana can cause slower reaction time among drivers and reduced coordination.