EMD GP50

The EMD GP50 entered production in 1980 as Electro-Motive Division's answer to the growing demand for higher-horsepower four-axle road switchers. The first units were delivered to the Chicago and North Western Railway during the summer of that year, inaugurating what would become a five-year production run. Much of the technology incorporated into the GP50 had been developed and proven through the experimental GP40X program, which served as a testbed for several of the design's most significant advances. Over the course of its production run, EMD built 278 examples of the type, with customers including the Burlington Northern, the St. Louis-San Francisco Railway, and several other major North American railroads. The GP50 holds a notable place in locomotive history as the first production series to be equipped with a microprocessor control system and the first to feature EMD's Super Series wheelslip control as a standard offering. The Super Series technology employed a Doppler radar unit mounted beneath the front coupler pocket to measure actual ground speed and adjust power distribution to each axle accordingly, yielding adhesion improvements of at least 33 percent compared to conventional locomotive designs. These innovations helped establish a template for the electronically sophisticated locomotives that would follow in subsequent decades. The later careers of many GP50s involved significant rebuilding programs. Beginning in 2004, BNSF undertook a program of rebuilding and derating its GP50 fleet to 2,500 horsepower, reclassifying the resulting units as GP25s and deploying many of them in remote control service. Norfolk Southern pursued a different course, rebuilding 28 of its GP50s into low-emission GP33ECO units between 2015 and 2016 and converting one additional example into a GP59ECO, extending the useful service life of the type while substantially reducing exhaust emissions.

The GP50 is powered by the 16-cylinder EMD 645F3B prime mover, producing 3,500 horsepower and driving a B-B wheel arrangement through a DC traction system. The 645F3B incorporated numerous refinements over earlier versions of the 645 engine family, including a strengthened crankcase, a new turbocharger design, laser-hardened cylinder liners, rocking piston pins, and one-half-inch-diameter plunger injectors. The traction motors fitted to the GP50 were the new D87 model, rated at a continuous 1,170 amperes compared to the 1,150 amperes of the predecessor D77, and featuring revised interpole and main field coils using approximately 16 percent more copper. These motors were connected in permanent parallel configuration to a new AR15 alternator rated at 4,680 amperes. Despite its increased power output relative to earlier four-axle EMD designs, the GP50 retained the same overall length of 59 feet 2 inches shared by the GP38, GP39, and GP40 series, achieved in part through a redesigned underframe using a lighter yet deeper sill. The locomotive also incorporated a revised exhaust system and Q-type cooling fans to comply with federal noise regulations that took effect in January 1980.

Models by: Athearn · Bachmann · Walthers