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 during the Great Depression, from which it never recovered, and it was forced into bankruptcy in 1954.

Its right-of-way between Jersey City and Newark is located in close proximity to Conrail, NJ Transit, and Amtrak trackage, and it shares the Dock Bridge with intercity and commuter trains.

[22] Revenue service started between Hoboken Terminal and 19th Street at midnight on February 26, 1908, when President Theodore Roosevelt pressed a button at the White House that turned on the electric lines in the uptown tubes (the first train carrying passengers, all selected officials, had run the previous day).

[35][36] A stop at Summit Avenue (now Journal Square), located between Grove Street and Manhattan Transfer, opened in April 1912 as an infill station on the Newark-Hudson Terminal line, though only one platform was in use at the time.

The New York and New Jersey Railroad Company received perpetual rights to dig under Christopher and Ninth Streets eastward to either Second Avenue or Astor Place.

[8]: 22 [4] In February 1909 the H&M announced plans to extend its Uptown Tubes northeast to Grand Central Terminal, located at Park Avenue and 42nd Street.

[39] The Interborough Rapid Transit Company (IRT), a competitor to the H&M, proposed to connect its Lexington Avenue line to the H&M at Grand Central, Astor Place, and Fulton Street–Hudson Terminal once the planned system was complete.

[8]: 56 [51] The Summit Avenue station was renovated and rededicated as "Journal Square" in 1929; the railroad's powerhouse in Jersey City shut down later that year, as its system could now draw energy from the greater power grid.

[76] In January 1973, the Port Authority released plans to double the route mileage of the PATH system[71] with an extension from Newark Penn Station to Plainfield, New Jersey.

[80] Eventually, the administration agreed to back it,[81] but in 1977, the U.S. Supreme Court ruled that the two state legislatures had violated the U.S. Constitution's Contract Clause by repealing a covenant in the 1962 bond agreements in order to make the extension possible.

[99] By 1992, the Port Authority had spent $900 million on infrastructure improvements, including repairing tracks, modernizing communications and signaling, replacing ventilation equipment, and installing elevators at seven stations per the Americans with Disabilities Act of 1990 (ADA).

[113] Exchange Place, the next-to-last station before World Trade Center, had to be closed as well because trains could not turn around there;[114] it had also suffered severe water damage.

The stub, the "Penn Pocket", had been built to take PRR commuters from Harborside Terminal on short turn World Trade Center to Exchange Place runs.

[123] The construction of the permanent four-platform World Trade Center Transportation Hub started in July 2008, when the first prefabricated "ribs" for the pedestrian walkway under Fulton Street were installed.

[136] The PATH station at Hoboken Terminal suffered major damage after floodwaters as high as eight feet (2.4 m) submerged the tunnels; it was closed for several weeks for $300 million worth of repairs.

Ward, as executive director, announced that PATH would be spending $321 million on communications-based train control (CBTC) with Siemens' Trainguard MT, upgrading its signal system for an increase in ridership.

In September 2019, service on the Newark–World Trade Center and Journal Square–33rd Street lines would be increased by 10 percent during rush hours, reducing the headway between trains from four minutes to three.

[181] In February 2014, the Port Authority's Board of Commissioners approved a 10-year capital plan that included the PATH extension to NJ Transit's Newark Liberty International Airport Station.

[186] In December 2014, the PANYNJ awarded a three-year, $6 million contract to infrastructure design firm HNTB to do a cost analysis of the Newark Airport extension.

[188][189] A presentation at two December 2017 public meetings[190] showed the new PATH station would include a park-and-ride lot and a new entrance from the nearby Dayton neighborhood.

The SmartLink was developed at a cost of $73 million, and initially was intended as a regional smart card that could be deployed on transit systems throughout the New York metropolitan area.

[236] PATH fare payment may also be made using single-ride, two-trip, and pay-per-ride MetroCards, the standard farecard of New York's Metropolitan Transportation Authority (MTA).

[247] In 2005, the Port Authority awarded a $499 million contract to Kawasaki to design and build 340 new PATH cars under the PA5 order to replace the system's entire existing fleet.

[3] With an average age of 42 years and some cars dating back as far as 1964, the fleet was the oldest of any operating heavy rail line in the United States.

Back-lit panels above the doors displayed the destination of that particular train: HOB for Hoboken, JSQ for Journal Square, NWK for Newark, 33 for 33rd Street, and WTC for World Trade Center.

Additionally, all PATH train operators must be federally certified locomotive engineers, and the agency must conduct more detailed safety inspections than other rapid transit systems.

These requirements increase PATH's per-hour operating costs relative to other rapid transit systems in the New York City and Philadelphia areas.

[255] PATH management has two principal passenger outreach initiatives: the "PATHways" newsletter, distributed for free at terminals, as well as the Patron Advisory Committee.

[282] On trains bound for Newark or Hoboken from World Trade Center, a short, zoetrope-like advertisement was formerly visible in the tunnel before entering Exchange Place.

[286] The PATH system is also often used as a stand-in for the New York City Subway,[287] as in John Wick: Chapter 2 where it was portrayed as a "Broad Street bound Z train".