EMD GP-series

EMD GP-series
Name	EMD GP-series
Power type	Diesel-electric
Builder	Electro-Motive Division
Build date	1949–1972
Total produced	Approx. 2,962
Wheel arrangement	B-B
Prime mover	EMD 567; EMD 645
Operator	North American railroads; export operators

EMD GP-series

The EMD GP-series refers to a family of road-switcher diesel-electric locomotives built by Electro-Motive Division of General Motors for North American and export service between 1949 and 1972. These locomotives played a central role in the dieselization of United States and Canadian National Railway operations, serving mainline freight, yard, and branchline duties for carriers such as Pennsylvania Railroad, Santa Fe, Union Pacific Railroad, Canadian Pacific Railway, and Southern Pacific Transportation Company. The series combined a two-axle truck arrangement with flexible cab and hood designs derived from wartime and postwar EMD practice, influencing subsequent generations like the EMD SD-series and contemporaries from ALCO and Baldwin Locomotive Works.

Development and Design

EMD developed the GP-series following lessons from wartime projects like the World War II-era EMD FT and postwar demonstrators that informed interactions with customers such as Baltimore and Ohio Railroad and New York Central Railroad. The GP design emphasized a short hood and long hood hood-unit format, adopting the road-switcher concept pioneered by builders including Alco with its Alco RS-1. Early GP prototypes were tested against demonstrators from Fairbanks-Morse and GE Transportation to meet requirements set by Class I carriers like Chicago and North Western Transportation Company and Illinois Central Railroad. EMD incorporated modular components and standardized controls in collaboration with railroads including Norfolk and Western Railway to streamline maintenance and crew training.

Model Variants and Specifications

Variants ranged from the initial GP7 through GP9, GP18, GP20, GP28, GP30, and GP35, each using prime movers like the EMD 567 and later the EMD 645 series. Power outputs varied from about 1,500 hp in GP7 and GP9 models to 2,250 hp in some GP35s, with key technical differences including turbocharging (as in the GP20) and electrical system upgrades comparable to innovations from General Electric units supplied to Penn Central Transportation Company. Trucks and traction motors were supplied by subsidiaries and partners such as General Steel Castings and Westinghouse Electric Corporation on contemporaneous designs. Cab arrangements included high and low short hoods to meet safety and visibility preferences endorsed by unions including the Brotherhood of Locomotive Engineers and regulatory guidance from agencies like the Interstate Commerce Commission.

Production History and Operators

Production spanned EMD’s La Grange, Illinois, plant and involved major buyers across North America, with substantial orders from Atchison, Topeka and Santa Fe Railway, Chicago, Burlington and Quincy Railroad, and Missouri Pacific Railroad. Exports reached operators such as Ferrocarriles Nacionales de México and railways in Brazil and Mexico where subsidiaries of General Motors supported local maintenance. Mergers and consolidations—most notably those involving Penn Central and later Conrail—shaped GP-series allocation and rebuild programs. Shortline and regional operators including Arkansas Southern Railroad and Illinois Railway often acquired secondhand units, extending service lives well beyond initial retirements.

Technical Features and Innovations

The GP-series introduced or popularized features such as modular electrical cabinets influenced by practices in General Motors' Research Laboratories, dynamic braking options, and standardized control stands adaptable to multiple signaling systems used by carriers like New York, New Haven and Hartford Railroad. The adoption of turbocharging on the GP20 paralleled developments in the diesel engine industry and echoed efforts by companies like EMD to compete with Alco's 244 and Fairbanks-Morse 38D8-1/8 engines. Traction control, improved cooling packages, and frame-mounted air reservoirs represented iterative advances that informed later models such as the GP40 and road locomotives supplied to British Columbia Railway.

Service Use and Performance

GP units excelled in mixed-traffic roles, substituting for dedicated road or switcher motive power on routes operated by Southern Railway (U.S.), Rock Island Line, and Gulf, Mobile and Ohio Railroad. Their B-B wheel arrangement offered lower axle loads suitable for light-rail branchlines operated by entities like Boston and Maine Corporation and enabled effective use on heavily trafficked corridors managed by St. Louis–San Francisco Railway. Reliability and ease of maintenance contributed to long service lives; many units underwent midlife rebuilds by contractors including National Railway Equipment Company and owner shops at Union Pacific Railroad and Kansas City Southern Railway. Performance metrics such as starting tractive effort and continuous tractive effort were competitive with contemporaries from General Electric and influenced allocation decisions by operational planners at carriers like Canadian National Railway.

Preservation and Legacy

Numerous GP-series locomotives survive in museums, tourist operations, and shortline fleets, preserved by organizations such as the Illinois Railway Museum, California State Railroad Museum, National Railroad Museum (Green Bay, Wisconsin), and heritage lines like Durango & Silverton Narrow Gauge Railroad where applicable pieces interpret diesel transition history. Preservation efforts often involve donor parts sourced from active freight carriers including BNSF Railway and specialty shops tied to former railroad mechanical departments. The GP-series legacy endures in its influence on subsequent designs, industrial practices at Electro-Motive Division, and its iconic presence in film, photography, and model railroading communities represented by clubs like NMRA and manufacturers such as Athearn and Bachmann Industries.

Category:Diesel-electric locomotives