Even people who've never been to New York can tell you how to hail one of the iconic yellow cabs there. You just raise an arm and flag one down.
But the city wants to change that. Following the lead of cities like San Francisco and Washington, D.C., New York wants to permit passengers to use smartphone apps to find a cab.
Since Mayor La Guardia established New York's modern taxi system in 1937, there have been two big innovations in cab hailing: the whistle and the red light bulb on top of apartment building awnings.