linguistic:paraphrasing
Lines and routes

Many rapid transit systems run relatively static routings, so that a train "line" is more or less synonymous with a train "route". In New York City, routings change often, for various reasons. Within the nomenclature of the subway, the "line" describes the physical railroad track or series of tracks that a train "route" uses on its way from one terminal to another. "Routes" (also called "services") are distinguished by a letter or a number and "lines" have names. Trains display their route designation.

There are 28 train services in the subway system, including three short shuttles. Each route has a color and a local or express designation representing the Manhattan trunk line of the service. New York City residents seldom refer to services by color (e.g., "blue line" or "green line") but out-of-towners and tourists often do.

The 1, C, G, L, M, R, and W trains are fully local and make all stops. The 2, 3, 4, 5, A, B, D, E, F, N, and Q trains have portions of express and local service. J, Z, 6, and 7 trains vary by direction, day, or time of day. The letter S is used for three shuttle services: Franklin Avenue Shuttle, Rockaway Park Shuttle, and 42nd Street Shuttle.

Though the subway system operates on a 24-hour basis, during late night hours some of the designated routes do not run, run as a shorter route (often referred to as the "shuttle train" version of its full-length counterpart) or run with a different stopping pattern. These are usually indicated by smaller, secondary route signage on station platforms. Because there is no nightly system shutdown for maintenance, tracks and stations must be maintained while the system is operating. This work sometimes necessitates service changes during midday, overnight hours, and weekends.

When parts of lines are temporarily shut down for construction purposes, the transit authority can substitute free shuttle buses (using MTA Regional Bus Operations bus fleet) to replace the routes that would normally run on these lines. The Transit Authority announces planned service changes through its website, via placards that are posted on station and interior subway-car walls, and through its Twitter page.