NEW YORK -- New York City's lower 40 kph speed limit is now the law.

It went into effect Friday.

It applies to all locations where a maximum speed is not posted.

The measure is part of Mayor Bill de Blasio's ambitious traffic safety plan known as "Vision Zero" to reduce pedestrian and driver deaths.

The city is replacing about 3,000 speed signs.

The 40 kph speed limit affects about 90 per cent of the city's streets.