New York City's commuter rail network is the largest in North America. The rail network, connecting New York City to its suburbs, consists of the Long Island Rail Road, Metro-North Railroad, and New Jersey Transit. The combined systems converge at Grand Central Terminal and Pennsylvania Station and contain more than 250 stations and 20 rail lines. In Queens, the elevated AirTrain people mover system connects JFK International Airport to the New York City Subway and the Long Island Rail Road; a separate AirTrain system is planned alongside the Grand Central Parkway to connect LaGuardia Airport to these transit systems. For intercity rail, New York City is served by Amtrak, whose busiest station by a significant margin is Pennsylvania Station on the West Side of Manhattan, from which Amtrak provides connections to Boston, Philadelphia, and Washington, D.C. along the Northeast Corridor, as well as long-distance train service to other North American cities.

How many rail lines are there on New York City's commuter rail network?