An SD50 operated by Kansas City Southern Railway.

(Jungmeister, CC BY-SA 3.0 <>, via Wikimedia Commons)



The EMD SD50 is a 3,500-horsepower (2,610 kW) diesel-electric locomotive built by General Motors Electro-Motive Division. It was introduced in May 1981 as part of EMD's "50 Series"; production ceased in January 1986. The SD50 was a transitional model between EMD's Dash 2 series which was produced throughout the 1970s and the microprocessor-equipped SD60 and SD70 locomotives. A total of 431 were built.



The SD50 was produced in response to increasingly tough competition from GE Transportation, whose Dash 7 line was proving quite successful with railroads. While EMD's SD40-2 was a reliable and trusted product, GE's line included locomotives up to 3,600 hp (2,685 kW) with more modern technology, as well as very competitive finance and maintenance deals. EMD responded throughout the SD50 program by offering discounts on large orders.

The GM-EMD locomotives that immediately preceded the SD50, the 3,600 hp (2,685 kW) SD45 and SD45-2, used huge, 20-cylinder engines that consumed large amounts of fuel and suffered from reliability problems when first introduced. Demand for the 45 series dropped sharply after the 1970s fuel crisis. The SD50 used an updated version of the V16 645 from the SD40-2, uprated to 3,500 hp (2,600 kW) at 950 rpm from 3,000 hp (2,240 kW) at 900 rpm, and uprated again in November 1984 to 3,600 hp (2,685 kW). This proved to be a step too far; the 50 series models were plagued by engine and electrical system problems which harmed EMD's sales and reputation.

Compared with their predecessors, the SD50 had a longer frame and a substantially longer long hood. In addition, the resistors for the dynamic brake grid were moved from their location on previous models above the prime mover to a new, cooler location in front of the engine compartment air intakes, closer to the electrical switchgear. This increased their separation from other systems, simplifying maintenance for the prime mover and the electrical system.

One former SD50 engineer praised the locomotives' wheel-slip control system and dynamic braking power, stating "they were able to give more adhesion than a SD40-2".


Chessie System (C&O) SD50 locomotive No. 8634 at Connellsville, PA, 29 May 1986.

(JesseSvoboda, CC BY-SA 3.0 <>, via Wikimedia Commons)



The SD50 is powered by V16 16-645F3 series diesel engine driving either an EMD AR11A-D14 or an EMD AR16A-D18 traction alternator. The power generated by the traction alternator drove 6 EMD D87 traction motors rated at 1170 amps each.

The SD50 was available with multiple traction motor gearing ratios and wheel sizes, the most common of which was the 70:17 ratio with 40-inch (1,016 mm) wheels, which allowed for a top speed of 70 mph (110 km/h). Other gearing options for the SD50 with 40-inch (1,016 mm) wheels included 69:18 for 76 mph (122 km/h), 67:19 for 82 mph (132 km/h) and 66:20 for 88 mph (142 km/h). The SD50 was also available with 42-inch (1,067 mm) wheels.

The SD50 was also available with either HT-C trucks (identified with a hydraulic shock on the side of the middle axle of each truck) or the earlier Flexicoil trucks. Some investigators implicated the HT-C truck in derailments of Amtrak's SDP40Fs, so Conrail chose the Flexicoil C trucks for their SD40-2s and their first order of SD50s—the only customer to do so. The controversy surrounding the HT-C truck was eventually disproved, and Conrail chose HT-C trucks for their second order of SD50s and SD60s.


NS SD50 No. 5443 (Ex-Conrail No. 6776).

(Railfan Jack at en.wikipedia, CC BY-SA 3.0 <>, via Wikimedia Commons)



The SD50S ("short frame") were prototype units built in December 1980. They were shorter than production locomotives by approximately 2 feet (0.61 m). There were six SD50Ss built, all of which were sold to the Norfolk & Western and eventually passed to Norfolk Southern. They were withdrawn in the early 2000s as non-standard. Two were rebuilt in 2008 as "SD40E" models by Norfolk Southern's Juniata Shops, along with several standard length SD50s.

The SD50S designation was also used for five locomotives built by EMD Australian licensee Clyde Engineering, Adelaide for Hamersley Iron. Shorter than production SD50s, they were equipped with a special double cab roof for insulation against the hot Australian desert sun in the Pilbara region. Withdrawn in November 1995, they were sold to National Railway Equipment Company and exported to the United States in February 1999 and used in national lease service. They were subsequently sold to the Utah Railway in June 2001. In June 2017, 6063 and 6064 were sold to the Chicago, Fort Wayne & Eastern Railroad, 6064 was relocated by Genesee & Wyoming to the Indiana & Ohio Railway and renumbered 5017.


CN SD50F No. 5438 with a coal train at Clolell, BC, Canada, September 14, 1987.

(Photo by Roger Puta, courtesy Marty Bernard, railfan 44, Public domain, via Wikimedia Commons)



The SD50F was a Canadian cowl unit version equipped with a "Draper taper" (inset section aft of cab for limited rear visibility). Sixty were built for the Canadian National Railway as road numbers 5400–5459. Early engine problems resulted in a temporary down-rating to 3,300 horsepower (2,500 kW). Eventually the units were re-rated to 3,500 horsepower (2,600 kW); however, like their U.S. cousins, they continued to suffer from relatively low reliability, frequently suffering engine, power assembly, and crankshaft failures.


Original owners


Railroad Qty. Road numbers Notes
Baltimore & Ohio (Chessie System) 20 8576–8595
Chicago & North Western 35 7000–7034 7009 donated to the Illinois Railway Museum
Chesapeake & Ohio (Chessie System) 43 8553–8575, 8624–8643
Conrail 135 6700–6834
Denver & Rio Grande Western 17 5501–5517
Kansas City Southern Railway 10 704–713
Missouri Pacific Railroad 60 5000–5059
Seaboard System Railroad 81 8500–8552, 8596–8623
Norfolk Southern 20 6506–6525
Hamersley Iron 5 6060–6064


Railroad Qty. Road numbers Notes
Norfolk & Western Railway 6 6500–6505 SD50S short frame


Railroad Qty. Road numbers Notes
Canadian National 60 5400–5459 Cowl units


A number of SD50s have been rebuilt into the equivalent of SD40-2s. The Dash 2 features are already contained within the SD50. The units are derated from 3,500 hp (2,600 kW) at 950 rpm to 3,000 hp (2,200 kW) at 900 rpm. This is actually a quite simple change to the locomotive's Woodward PGE engine governor.


C&NW EMD SD50 No. 7008, sister to the only preserved unit (No. 7009), at Proviso Yard, Chicago in 1987.

(Gary Todd from Xinzheng, China, CC0, via Wikimedia Commons)



In late October 2022, the Illinois Railway Museum acquired former Chicago & North Western No. 7009, believed by the museum to be the first preserved SD50.



Type and origin
Power type: Diesel-electric
Builder: Electro-Motive Diesel, General Motors Diesel, Clyde Engineering
Build date: December 1980 – July 1987
Total produced: 431
Gauge: 4 ft 8+1⁄2 in (1,435 mm) standard gauge
Length: 71 ft 2 in (21.69 m) over the coupler pulling faces
Prime mover: EMD 645
Engine type: V16 diesel
Alternator main: AR11
Cylinders: 16
Performance figures
Power output: 3,500 hp (2,610 kW) at 950 rpm; increased to 3,600 hp (2,685 kW) November 1984.
Operators: See Original buyers list above
Disposition: Some in service, some retired, one preserved