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 K4 was a class of 425 4-6-2 steam locomotives built between 1914 and 1928 for the PRR, where they served as the primary main line passenger steam locomotives on the entire PRR system until late 1957.
The Pennsylvania Railroad (PRR) class T1 duplex-drive 4-4-4-4 steam locomotives, introduced in 1942 with two prototypes and later in 1945-1946 with 50 production examples, were the last steam locomotives built for the PRR and arguably its most controversial. They were ambitious, technologically sophisticated, powerful, fast and distinctively streamlined by Raymond Loewy. However, they were also prone to wheelslip both when starting and at speed, in addition to being complicated to maintain and expensive to run. The PRR decided in 1948 to place diesel locomotives on all express passenger trains, leaving unanswered questions as to whether the T1's flaws were solvable, especially taking into account that the two prototypes did not have the problems inherent to the production units.
A 4-4-4-4 steam locomotive, in the Whyte notation for describing locomotive wheel arrangements, has a four-wheel leading truck, two sets of four driving wheels, and a four-wheel trailing truck. While it would be possible to make an articulated locomotive of this arrangement, the only 4-4-4-4s ever built were duplex locomotives—with two sets of cylinders driving two sets of driven wheels in one rigid frame, essentially a 4-8-4 with divided drive.
The Pennsylvania Railroad's class B6 was its most successful class of switcher locomotive, 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 PRR S1 class steam locomotive was a single experimental duplex locomotive of the Pennsylvania Railroad. It was designed to demonstrate the advantages of duplex drives espoused by Baldwin Chief Engineer Ralph P. Johnson. The S1 class was the largest rigid frame passenger steam locomotive ever built. The streamlined Art Deco styled shell of the locomotive was designed by Raymond Loewy.
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 mainly 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 class Q1, #6130, was a single experimental steam locomotive designed for dual service. The locomotive entered service in 1942, and retired in 1949 after accumulating a relatively low 165,000 service miles.
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 Class E6 was the final type of 4-4-2 "Atlantic" locomotive built for the company, and second only to the Milwaukee Road's streamlined class A in size, speed and power. Although quickly replaced on the fastest trains by the larger K4s Pacifics, the E6 remained a popular locomotive on lesser services and some lasted until the end of steam on the PRR. One, #460, called the Lindbergh Engine, is preserved at the Railroad Museum of Pennsylvania. It was moved indoors to begin preparations for restoration on March 17, 2010. On January 10, 2011, PRR #460 was moved to the museum's restoration shop for a two- to three-year project, estimated to cost $350,000. The engine is listed in the National Register of Historic Places.
Pennsylvania Railroad Class L1s were 2-8-2 "Mikado"-type steam locomotives that were used on the Pennsylvania Railroad during the early twentieth century. These 574 locomotives were manufactured between 1914 and 1919 by the railroad's own Juniata Shops as well as the Baldwin Locomotive Works (205) and the Lima Locomotive Works (25).
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.
Pennsylvania Railroad No. 1223 is a D16sb class 4-4-0 "American" type steam locomotive built in November 1905 for the Pennsylvania Railroad by their own Altoona Works for passenger service. After being retired from active service in 1950, the locomotive ran excursion trains on the Strasburg Rail Road outside of Strasburg, Pennsylvania from 1965 to 1989 when it was removed from service requiring firebox repairs. Currently, the locomotive is still on static display at the Railroad Museum of Pennsylvania outside of Strasburg. It was listed on the National Register of Historic Places in 1979. No. 1223 is the only surviving example of the Pennsylvania Railroad's D16sb class.
Pennsylvania Railroad 1737 was a 4-6-2 Pacific type K4 class steam locomotive built in 1914 as the first of its class and would haul heavier passenger trains that the smaller E class 4-4-2 Atlantics could not handle such as the PRR's flagship passenger train, the Broadway Limited. In the 1930s, as the PRR had increased passenger service time tables, the trains became longer and heavier than a single K4s could handle, necessitating double-heading with a second engine. The "Standard Railroad Of The World" made attempts to replace the 1737 and its classmates with larger, more powerful classes including: K5, S1, and the T1, none of which were successful; thus, the K4s continued hauling passenger trains until the Pennsylvania Railroad replaced steam locomotives with the increasingly-popular and less-costly diesel-electric locomotives in 1957.
The Pennsylvania Railroad's class H6, H6a, and H6b steam locomotives were of the 2-8-0 "Consolidation" freight type, the most numerous class on the railroad with 1,707 units and the second most prolific 2-8-0 class in North America, with the USATC S160 class rostering 88 units more. The three subclasses differed as follows:
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.
Pennsylvania Railroad's E1 class comprised three experimental 4-4-2 "Atlantic" locomotivess built in 1899 to compete with the Reading Railroad on the Philadelphia, Pennsylvania, to Atlantic City, New Jersey, high-speed seashore passenger train service. These engines were designed as cab-center or camelback locomotives with wide fireboxes and 80 in (2,032 mm) drivers that carried 50,000 lb (22,680 kg) per axle. They proved capable in fast service but the inherent danger of separating the engineer from the fireman was unacceptable to the PRR so they were sold to their subsidiary the Long Island Rail Road in 1903. While the camelback design was unfavorable the Atlantic style proved to be everything the Pennsylvania Railroad needed at that time. They went on to acquire 596 additional units over the next fifteen years.
Pennsylvania Railroad 7002 is a E7s class 4-4-2 "Atlantic" type steam locomotive built for the Pennsylvania Railroad by their own Altoona Works in August 1902. Today, it is on display at the Railroad Museum of Pennsylvania outside of Strasburg, Pennsylvania in the United States. Originally No. 8063, the PRR renumbered it to No. 7002 after the original, claimed to be a land-speed-record-setter, was scrapped. It is the only survivor of its class and was listed on the National Register of Historic Places in 1979.
A duplex locomotive is a steam locomotive that divides the driving force on its wheels by using two pairs of cylinders rigidly mounted to a single locomotive frame; it is not an articulated locomotive. The concept was first used in France in 1863, but was particularly developed in the early 1930s by the Baldwin Locomotive Works, the largest commercial builder of steam locomotives in North America, under the supervision of its then chief engineer, Ralph P. Johnson.
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.
