The Pennsylvania Railroad had operated a specially designed car constructed on a flat car. It's purpose was to accurately measure the distance above and/or adjacent to the tracks of bridges, tunnels, stations and rock cuts, etc.
The demaind for increased speed to shorten travel time in both present day industry and the business world has caused the railroad to provide more clearance for movement of equipment. The trend to larger equipment such as locomotives, passenger & freight cars and larger loads in open top cars has made the gathering of clearance information an area of growing importance. The Pennsylvania has spent millions of dollars to increase clerances for handling traffic. In the 1950s alone, the Panhandle Division tunnel project between Pittsburgh, Pa., and Dennision, Oh., cost over $8 million.
The Z74 series were the most common of the Pennsy's business cars. However, their history is also the most convoluted. Over their lives, individual cars were reclassified, renumbered, and renamed many times. To make matters worse, for the historian, names were often re-used among one or more physical cars. The following documentation represents a "best effort" to piece together the physical car histories. A number in parenthesis indicates the iteration of use of a specific car number.
In HO scale, Bachmann offers a "heavyweight observation" car that is actually an early era version of a PRR Z74 business car (no evaluation of sub-class offered).
The ALCO S-1 and S-3 were 660 horsepower switcher diesel-electric locomotives produced by ALCO and their Canadian subsidiary Montreal Locomotive Works (MLW). The two locomotives differed only in trucks, with the S-1 using ALCO's own Blunt trucks, and the S-3 using AAR type A switcher trucks. The S-1 was built between April 1940 and June 1950, with a total of 543 completed, while the S-3 was constructed between February 1950 and November 1953 (MLW until 1957) with total sales of 300.
The Erie-built was the first streamlined, cab-equipped dual service diesel locomotive built by Fairbanks-Morse, introduced as direct competition to such models as the ALCO PA and EMD E-unit. As F-M lacked the space to manufacture the units in their own plant, the work was subcontracted out to General Electric, which produced the locomotives at its Erie, Pennsylvania, facility, thereby giving rise to the name "Erie-built."
The Baldwin VO-660 was a diesel-electric locomotive switcher built by Baldwin Locomotive Works between April, 1939 and May, 1946. The 197,520–203,980 lb units were powered by a six-cylinder diesel engine rated at 660 horsepower, and rode on two-axle AAR Type-A switcher trucks in a B-B wheel arrangement. 142 examples of this model were built for American railroads, along with the United States Navy. Baldwin replaced the VO-660 with the model DS-4-4-660 in 1946.
The GE 44-ton switcher is a 4-axle diesel-electric locomotive built by General Electric between 1940 and 1956. It was designed for industrial and light switching duties, often replacing steam locomotives that had previously been assigned these chores. This locomotive's specific 44-short ton weight was directly related to one of the efficiencies the new diesel locomotives offered compared to their steam counterparts: reduced labor intensity. In the 1940s, the steam to diesel transition was in its infancy in North America, and railroad unions were trying to protect the locomotive fireman jobs that were redundant with diesel units. One measure taken to this end was the 1937 so-called "90,000 Pound Rule", a stipulation that locomotives weighing 90,000 pounds – 45 short tons – or more required a fireman in addition to an engineer on common carrier railroads. Industrial and military railroads had no such stipulation. The 44-ton locomotive was born to skirt this requirement. Other manufacturers also built 44-ton switchers of center-cab configuration. 276 examples of this locomotive were built for U. S. railroads and industrial concerns, four were exported to Australia in 1944, 10 were exported to Canada, 10 were exported to Cuba, one was exported to the Dominican Republic, five were exported to France, three were exported to India, six were exported to Mexico, five were exported to Saudi Arabia, one was exported to Sweden, two were exported to Trinidad, 10 were exported to Uruguay, and 57 were built for the U. S. Military.
The EMD SW1 is a 600-horsepower diesel-electric switcher locomotive built by General Motors' Electro-Motive Corporation (later Division) between December 1938 and November 1953. Final assembly was at EMD's plant at LaGrange (McCook) Illinois. The SW1 was the second generation of 3,402 cu in (55.75 L) switcher from EMD, succeeding the SC (cast frame) and SW (welded frame). The most significant change from those earlier models was the use of an engine of EMD's own design, the then-new 567 engine, here in 600 hp V6 form. 661 locomotives of this design were built, no SW1s were built after March 1943 until production started again in September 1945.
Like most long-running locomotive models, a number of changes were made to the SW1 over its production life. Internally, the post-war locomotives were somewhat improved, and used the 567A engine.
The FM H-10-44 was a yard switcher produced by Fairbanks-Morse from August, 1944–March, 1950. The units featured a 1,000-horsepower, six-cylinder opposed piston engine prime mover, and were configured in a B-B wheel arrangement mounted atop a pair of two-axle AAR Type-A switcher trucks, with all axles powered. Many H-10-44s received modifications that increased their horsepower rating to 1,200 hp.
The FM H-16-44 was a road-switcher produced by Fairbanks-Morse from April 1950 – February 1963. The locomotive shared an identical platform and carbody with the predecessor Model FM H-15-44 (but not the FM H-20-44 end cab road switcher which used a different carbody and frame and a larger prime mover), and were equipped with the same eight-cylinder opposed piston engine that had been uprated to 1,600 horsepower. The H-16-44 was configured in a B-B wheel arrangement, mounted atop a pair of two-axle AAR Type-B road trucks with all axles powered. In late 1950, the AAR trucks were almost exclusively replaced with the same units found on the company's "C-liner" locomotives.