This is from TA Bulletin of NY
"The speed limit in New York City, unless otherwise posted, is 30 mph. Speeding, however, is rampant throughout the city and is in fact encouraged in many ways.
For one, most NYC streets are actually designed to accommodate vehicle speeds in excess of 35 mph.
Second, many "signal progressions" or the timing of consecutive traffic lights, are calibrated so that motorists obeying the speed limit see many more red lights than motorists who speed.
To encourage motorists to obey the speed limit, the city should first design roads for their posted speed (making lanes more narrow, for example) and second change signal timing so that speeding motorists are not rewarded with more green time.
Finally, in many European cities, speed limits are being lowered because at lower speeds traffic flow is often improved as many intersections, where bottlenecks occur, can actually process more traffic at lower speeds.
A more compelling reason to lower speed limits is to save lives: when a car moving at 20mph impacts a pedestrian, the pedestrian only dies 5% of the time. At 30mph, the chance of death jumps to 45% and at 40mph, 85% of pedestrians struck will die. "
