One of the strangest quirks of New York law is that city officials can't actually regulate speed on the city's streets. The right to set the speed limit rests almost entirely in Albany with the state legislature, a stubborn reality that has long blocked efforts to slow traffic on pedestrian-filled thoroughfares.
Now, advocates and elected officials are mounting a serious push to change that. New bills introduced in the state Assembly and Senate would give the New York City Council the power to reduce the speed limit by 10 mph on residential streets.
Currently, the limit on these streets is 30 mph, except where marked. It can't be lowered by more than five mph, except in school zones or with physical traffic-calming measures like speed bumps (the city has also designated a couple of special "slow zones").
This, however, is not a strange quirk but consistent with the political interests that established and have supported the domination of the car in urban planning. You must understand that a slower speed limit (20 mph) increases the risk of fees and delays for the driver at the expense of pedestrian safety. But the whole thinking up to now has been to make the experience of driving pleasant and affordable.