Locomotive classification on the Pennsylvania Railroad took several forms. Early on, steam locomotives were given single-letter classes. As the 26 letters were quickly assigned, that scheme was abandoned for a more complex system. This was used for all of the PRR's steam locomotives, and — with the exception of the final type bought — all electric locomotives also used this scheme.
The Pennsylvania Railroad (PRR) K4 4-6-2 "Pacific" was its premier passenger-hauling steam locomotive from 1914 through the end of steam on the PRR in 1957.
The Pennsylvania Railroad's class B6 was its most successful class of switcher, or as the PRR termed them "shifter". The PRR preferred the 0-6-0 wheel arrangement for larger switchers, whereas on other railroads the 0-8-0 gained preference. The PRR generally used 2-8-0s when larger power was required.
The New York Tunnel Extension is a combination of railroad tunnels and approaches from New Jersey and Long Island to Pennsylvania Station in Midtown Manhattan.
The Pennsylvania Railroad's class P5 comprised 92 mixed-traffic electric locomotives constructed 1931–1935 by the PRR, Westinghouse and General Electric. Although the original intention was that they work many passenger trains, the success of the GG1 locomotives meant that the P5 class were mostly used on freight. A single survivor, prototype #4700, is at the National Museum of Transportation in St Louis, Missouri.
The Pennsylvania Railroad's class O1 comprised eight experimental boxcab electric locomotives built in 1930 and 1931. They were built in preparation for the New York to Washington Electrification project. They had the wheel arrangement classified as 4-4-4 in the Whyte notation. Although successful, they were not powerful enough for the railroad's increasingly heavy trains. For production, the PRR chose to concentrate on the P5 class, effectively an enlarged and more powerful version of the O1 with an additional pair of driving wheels.
The Pennsylvania Railroad's class DD2 was a single prototype electric locomotive never placed into series production. It was intended as an improved and simplified GG1 for use on the planned, but never built, extension of the PRR's electrification west of Harrisburg, Pennsylvania. The one locomotive produced was numbered #5800 and used in regular Baltimore tunnel helper service until it was scrapped in September 1962.
The Great Northern Railway's class Y-1 comprised eight electric locomotives with AAR 1-C+C-1 wheel arrangements. The locomotives were used on the 73-mile (117 km) electrified portion of the railroad, from Wenatchee, Washington to Skykomish, Washington, including the Cascade Tunnel.
Pennsylvania Railroad class E2b comprised six experimental B-B electric locomotives built for the railroad by General Electric.
The Pennsylvania Railroad's class L5 were the railroad's second generation of production electric locomotives after the DD1, and the last to use a jackshaft and side rods to drive the wheels. The L5 was a single-unit locomotive instead of the twin-unit DD1. The wheel arrangement in Whyte notation was 2-4-4-2, or 1-B-B-1 in the AAR scheme. Twenty five were built in 4 distinct subclasses. The lead unit of the class was equipped for AC operation with an overhead pantograph, while the other 24 were third rail DC units to work on the existing PRR third rail electrification in the New York area.
The Pennsylvania Railroad's class B1 comprised 42 switcher-type electric locomotives built between 1926 and 1935. They were of 0-6-0 wheel arrangement in the Whyte notation with 700 horsepower. As built, the first 28 locomotives in the 1926 order formed semi-permanently coupled pairs grouped in three classes.
The Pennsylvania Railroad's class AA1 comprised two experimental electric locomotives constructed in 1905 by the company's own Altoona Works with the assistance of Westinghouse. Intended as testbeds as the PRR began its electrification project, both locomotives remained service into the 1930s.
Pennsylvania Railroad's Odd D #10003 was an experimental electric locomotive built in 1907 by Baldwin and Westinghouse. It had a 4-4-0 wheel arrangement in the Whyte notation, or 2-B in the AAR scheme. On the PRR, class D was assigned to 4-4-0 locomotives. Production classes of locomotive were assigned a number after the letter, but one-off locomotives were simply designated "Odd".
Railroad electrification in the United States began at the turn of the 20th century and comprised many different systems in many different geographical areas, few of which were connected. Despite this situation, these systems shared a small number of common reasons for electrification.
Class D16 on the Pennsylvania Railroad was their final development of the 4-4-0 "American" type of steam locomotive. A total of 429 of these locomotives were built at the PRR's Juniata Shops, spread across five subclasses; some had 80 in (2,030 mm) diameter driving wheels for service in level territory, while others had 68 in (1,730 mm) drivers for mountainous terrain. In the pre-1895 scheme, these locomotives were second class L.
The Pennsylvania Railroad's steam locomotive class D1 comprised thirteen 4-4-0 locomotives for express passenger service, constructed at the railroad's own Altoona Works during 1868–1872. They were the first standardized class of locomotives on the railroad and shared many parts with other standard classes.
The Pennsylvania Railroad's MP54 was a class of electric multiple unit railcars. The class was initially constructed as an unpowered, locomotive hauled coach for suburban operations, but were designed to be rebuilt into self-propelled units as electrification plans were realized. The first of these self-propelled cars were placed in service with the PRR subsidiary Long Island Rail Road with DC propulsion in 1908 and soon spread to the Philadelphia-based network of low frequency AC electrified suburban lines in 1915. Eventually the cars came to be used throughout the railroad's electrified network from Washington, D.C. to New York City and Harrisburg, Pennsylvania.
The Pennsylvania Railroad G5 is a class of 4-6-0 steam locomotives built by the PRR's Juniata Shops in the mid-late 1920s. It was designed for passenger trains, particularly on commuter lines, and became a fixture on suburban railroads until the mid-1950s. The G5 was the largest and most powerful 4-6-0 locomotive, except for a single Southern Pacific 4-6-0 that outweighed it by 5,500 lb.
The Pennsylvania Railroad's class A5s was the largest class of 0-4-0 steam locomotives. The Pennsylvania Railroad built 47 in its Juniata Shops between 1916–1924. They were all retired by 1957. One is preserved at the Railroad Museum of Pennsylvania.
The Pennsylvania Railroad's class K29s comprised a single experimental 4-6-2 "Pacific" type steam locomotive. Constructed by Alco-Schenectady, it was given road number 3395. Although only one demonstrator was constructed, the K29s would become the basis for the highly successful K4s Pacifics and L1s Mikados. The lone example spent most of its life on the PRR's Pittsburgh division main line and was retired around 1929.
