It's time to slow down behind the wheel as the city's new default speed limit officially went into effect Friday in all five boroughs.

The limit is now 25 mph on all city streets, down from 30 mph, unless otherwise posted.

NYPD officers will be on alert, with help from traffic cameras, to issue tickets to drivers caught going too fast. Fines can range anywhere from $150 all the way up to $600 depending on the speed and prior violations. Points on a license are also possible.

Department of Transportation workers handed out fliers to let drivers know that the new speed limit is officially in effect.

The reduced speed limit is the foundation of Mayor Bill de Blasio's Vision Zero initiative, which aims to completely eliminate all traffic-related fatalities. He signed the lowered limit into law just last month in hopes of making the city a safer place for all pedestrians, drivers and cyclists.

Officials say the 5 mph decrease makes a big difference because if someone gets hit by a car going 25 instead of 30 mph that person is twice as likely to survive.