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Port Authority Trans-Hudson (PATH) is a 13.8-mile (22.2 km) rapid transit system in the northeastern New Jersey cities of Newark, Harrison, Jersey City, and Hoboken, as well as Lower and Midtown Manhattan in New York City. It is operated as a wholly owned subsidiary of the Port Authority of New York and New Jersey. PATH trains run around the clock year round; four routes serving 13 stations operate during the daytime on weekdays, while two routes operate during weekends, late nights, and holidays. Its tracks cross the Hudson River through century-old cast iron tubes that rest on the river bottom under a thin layer of silt. It operates as a deep-level subway in Manhattan and the Jersey City/Hoboken riverfront; from Grove Street in Jersey City to Newark, trains run in open cuts, at grade level, and on elevated track.

The routes of the PATH system were originally operated by the Hudson & Manhattan Railroad (H&M), built to link New Jersey's Hudson Waterfront with New York City. The system began operations in 1908 and was fully built out in 1911. Three stations have since closed; two others were re-located after a re-alignment of the western terminus. From the 1920s, the rise of automobile travel and the concurrent construction of bridges and tunnels across the river sent the H&M into a financial decline from which it never recovered, and it was forced into bankruptcy in 1954. As part of the deal that cleared the way for the construction of the original World Trade Center, the Port Authority bought the H&M out of receivership in 1962 and renamed it PATH. In the 2000s and 2010s the system suffered considerably from disasters that affected the region, most notably the September 11 attacks and Hurricane Sandy. Both private and public stakeholders have proposed expanding PATH service in New Jersey, and an extension to Newark Liberty International Airport may be constructed in the 2020s.

Although PATH has long operated as a rapid transit system, it is legally a commuter railroad under the jurisdiction of the Federal Railroad Administration (FRA); its trackage between Newark and Jersey City is located in close proximity to Northeast Corridor trackage and shares the Newark Dock Bridge with intercity and commuter trains. All PATH train operators must therefore be licensed railroad engineers and extra inspections are required. PATH currently uses one class of rolling stock, the PA5, which was delivered in 2009–2011.