But now licensed cabdrivers in this city where the car remains king are facing their greatest competition in half a century, from new ride-sharing programs that use smartphone apps to connect drivers and passengers.

At the end of a night of drinking recently, rather than hailing a cab, Trisha DiFazio tapped an app called Lyft on her phone to summon a ride. Minutes later, a graduate student moonlighting as a driver pulled up in a Toyota S.U.V. with Lyft’s signature pink mustache affixed to its grille.

“This is so much cheaper than a cab, and so much easier,” said Ms. DiFazio, 31. “I absolutely think my friends drink and drive less because of this.”