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EMD SD50
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EMD SD50
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EMD SD50
An SD50 operated by Kansas City Southern Railway
Type and origin
Power typeDiesel-electric
BuilderElectro-Motive Diesel
General Motors Diesel
Clyde Engineering
ModelSD50
Build dateDecember 1980 – July 1987
Total produced431
Specifications
Configuration:
​
 • UICCo'Co'
Gauge1,435 mm (4 ft 8+1⁄2 in)
Length71 ft 2 in (21.69 m)
Fuel typeDiesel
Fuel capacity3,500 U.S. gal (13,000 L)
Lubricant cap.283 U.S. gal (1,070 L)
Coolant cap.250 U.S. gal (950 L)
Sandbox cap.56 cu ft (1,600 L)
Prime moverEMD 16-645F3B
RPM:​
 • Maximum RPM950
Engine typeV16 diesel
AspirationTurbocharged
Alternatormain : AR16/D18 (3,500), AR11 (3,600)
Traction motorsEMD 87Y (3,500), EMD 87A (3,600)
Cylinders16
TransmissionDiesel-electric
Gear ratio70:17
MU workingYes
Loco brakeWestinghouse, Dynamic brake
Train brakesAir braked
Performance figures
Maximum speed70 mph (110 km/h)
Power output3,500 hp (2,610 kW) at 950 rpm; increased to 3,600 hp (2,685 kW) November 1984.
Career
OperatorsSee Original buyers
DispositionSome in service, some retired, one preserved

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.[1]

History

[edit]

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".[2]

Technical

[edit]

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.

SD50S

[edit]

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.

NS 5443, an SD50

The SD50S designation was also used for five locomotives built by EMD Australian licensee Clyde Engineering, Adelaide for Hamersley Iron.[3] 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.[4] They were subsequently sold to the Utah Railway in June 2001.[5][6] 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 5016 and 5017.[7]

SDL50

[edit]
SRO 3524 and 3529, both SDL50s, at Riyadh East station in 2024.

The SDL50 ("L" standing for "lightweight")[8] was an export-only version of the SD50, designed to operate in harsh desert climates. The model was ordered only by the Saudi Government Railways Organization (later the Saudi Railways Organization, now Saudi Arabia Railways) in Saudi Arabia, for operation on the Dammam-Riyadh railroad. A total of 31 SDL50s were built in four batches from 1981 to 2005, numbered as the 3500-series.

Like most other SD50 models, the SDL50s use an EMD 16-645F3 prime mover rated at 3,500 horsepower (2,600 kW). Modifications for operation in the desert include extra-large air filters to keep out dust and sand, as well as special sealing in order to keep the train's traction motors and other components protected.[8]

SD50F

[edit]
CN 5438, an SD50F

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

[edit]
Railroad Qty. Road numbers Notes References
SD50
Baltimore & Ohio
(Chessie System) 		20 8576–8595
Chicago & North Western 35 7000–7034 7009 donated to the Illinois Railway Museum [2]
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
SD50S
Norfolk & Western Railway 6 6500–6505 SD50S short frame
SD50F
Canadian National 60 5400–5459 Cowl units
SDL50
Saudi Railways Organization 31 3500-3530 Modified for operation in the desert
Totals 523

Rebuilds

[edit]

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.

Preservation

[edit]

• Chicago & North Western #7009 is preserved at the Illinois Railway Museum in Union, Illinois. It is believed by the museum to be the first preserved SD50.[2]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

EMD SD50

View on Grokipedia
from Grokipedia
The is a six-axle, 3,500-horsepower diesel-electric built by the Electro-Motive Division (EMD) of , introduced in May 1981 as a high-power road freight unit designed to succeed the SD40-2 and conclude the use of EMD's long-serving 645-series engine. Powered by a 16-cylinder 645F3B prime mover, the SD50 featured innovative electronic controls, including ground-scanning for precise wheel slip detection, which improved traction by up to 25% and enabled greater , allowing three SD50s to handle the workload of four older locomotives. Weighing approximately 368,000 pounds with a length of 71 feet 2 inches, it delivered a starting of 92,000 pounds and a top speed of 65-70 mph, making it suitable for heavy-haul mainline service across North American railroads. Production ran from May 1981 to February 1986, with 431 standard SD50 units built primarily at EMD's plant, alongside variants like the cowl-bodied SD50S (6 units), wide-nose SDL50 (31 units for ), and 60 SD50F units for Canadian National. Major purchasers included (135 units), the Seaboard System (81 units), Norfolk Southern, and Kansas City Southern, with a total of around 492 locomotives sold to 12 railroads overall. Despite its advancements, the SD50 faced reliability challenges stemming from the 645 engine being pushed to its limits at 3,500 hp, leading to higher maintenance needs compared to predecessors; it served as a transitional model before the more robust SD60 arrived in 1984. Many SD50s remain in service today, particularly on Class II and III railroads, with some rebuilt or exported, underscoring their enduring role in freight operations.

Development and history

Design background

The Electro-Motive Division (EMD) of developed the SD50 as a successor to the successful SD40-2, seeking to deliver 3,500 horsepower from an upgraded version of the existing 16-cylinder 645 engine series to counter the rising market share of General Electric's Dash 7 series locomotives. This design choice emphasized evolutionary improvements over radical redesigns, avoiding the full integration that would define later models, while aiming for a cost-effective high-horsepower option in an era of intensifying competition. Positioned as a transitional locomotive between the Dash 2 series of the and the more advanced SD60 and SD70 models of the , the SD50 incorporated early electronic control elements but retained much of the analog systems from prior designs. Key engineering goals included boosting power output through enhanced turbocharging on the proven 645F3B prime mover, providing a reliable evolution that matched the performance of earlier 20-cylinder engines like the SD45 while prioritizing amid the oil crises. This approach addressed railroad operators' concerns over rising fuel costs by favoring a 16-cylinder configuration over less efficient larger engines, without requiring extensive retooling. Development began with initial testing and prototypes in the late , building on SD40X demonstrator units to evaluate the higher power demands of the uprated 645 engine, though engineers anticipated potential reliability issues from the increased stress on components. EMD formally introduced the SD50 in May 1981 as the inaugural model of its "50 Series," marking a strategic push to regain footing against GE's advancements.

Production timeline

The EMD SD50 entered production in December 1980 at the company's LaGrange, Illinois facility, beginning with six experimental SD50S cowl-bodied units delivered to the . Standard six-axle SD50 production commenced in May 1981 with an initial batch of 10 units for the , rated at 3,500 horsepower using the 16-645F3B V16 diesel engine. These early units marked EMD's push into higher-power road locomotives amid recovering rail industry demand following the recession. From 1981 to 1983, production ramped up with deliveries to key customers including , which received its first 40 units between November and December 1983, and other carriers seeking replacements for aging SD40-2 fleets. This phase saw steady output as EMD positioned the SD50 as a bridge model between the Dash 2 series and upcoming microprocessor-controlled designs, with approximately 100 units completed by the end of 1983. Missouri Pacific joined as an early major purchaser in late , ordering 60 units to bolster its and intermodal operations. In November 1984, EMD implemented a mid-production upgrade, increasing horsepower to 3,600 via refined on the 645F3C variant, paired with an upgraded AR11 and D87A traction motors for improved efficiency and . This enhancement applied to all subsequent standard SD50s, affecting over half of the total build and addressing initial performance feedback from operators. Production slowed in 1985–1986 due to emerging reliability concerns with the over-stressed 645-series and transitional electrical systems, which experienced , overheating, and control failures in service. EMD responded by establishing dedicated repair programs, but these issues eroded customer confidence and contributed to a shift in market dynamics. The final standard SD50 units rolled out in February 1986, with overall SD50-series production—including variants—extending to July 1987. A total of 431 standard SD50 locomotives were built, alongside 6 SD50S, 60 SD50F, and 31 SDL50 units. The model's troubles accelerated EMD's loss of market share to by the late 1980s, as GE's Dash 8 series gained favor for superior reliability and financing options, marking the first year GE outsold EMD in 1985.

Design and specifications

Engine and powertrain

The EMD SD50's prime mover is the EMD 16-645F3B, a 16-cylinder with a displacement of 10,570 cubic inches (173 liters), producing 3,500 horsepower (2,610 kW) at 950 rpm. This represents an evolution of the 645 series, incorporating a late exhaust timing design to enhance power output while maintaining the uniflow-scavenged for efficient . In November 1984, production models received upgrades including an improved and modified system, increasing output to 3,600 horsepower (2,700 kW) under the 645F3C designation; the power increase stemmed from optimized boost pressure and injection timing, allowing higher sustained loads without major redesign. The engine couples to an AR11 (initially AR16 on early units), which converts mechanical energy into electrical power for propulsion. This feeds six D87B DC traction motors—one per in the HTC truck assembly—each rated for 1,170 amps continuous, enabling a top speed of 65 mph (105 km/h) with a 62:15 gear ratio. Wheel slip control relies on an early electronic load regulator system, part of EMD's "Super Series" , which modulates excitation to prevent slippage during startup and acceleration, though it marked a transitional step from relay-based to partial governance. The fuel system supports a standard capacity of 3,500 US gallons (13,200 L) in a underframe , designed for extended heavy-haul runs. Despite these capabilities, the SD50's exhibited early flaws, including frequent cylinder liner and head failures due to stresses from the uprated 645 series operating near its limits, as well as overheating in the cooling and exhaust systems during prolonged high-demand operation. The shift to partial electronic controls also introduced glitches in wheel slip detection and response, stemming from unreliable integration of and nascent elements, which occasionally led to inconsistent power delivery and required field adjustments. Maintenance demands were elevated owing to turbocharger wear from sustained high boost; ensuring longevity in demanding freight service.

Body, chassis, and features

The EMD SD50 featured a conventional hood-type body design typical of Electro-Motive Division's six-axle road locomotives, with a narrow hood providing maintenance access to internal components and dynamic brake resistors housed in a step-up arrangement between the cab and the engine air intake for improved cooling efficiency. The body measured 71 feet 2 inches (21.69 m) in length over the couplers, 10 feet 3 inches (3.12 m) in width over the handrails, and 15 feet 7 inches (4.75 m) in height from the rail to the top of the cab, optimizing it for standard freight clearances while maintaining a low profile for stability. The chassis utilized a C-C truck configuration with HTC high-traction trucks, each spanning a 13-foot 7-inch (4.14 m) wheelbase and equipped with 40-inch (1,016 mm) diameter wheels, distributing 100% of the locomotive's weight onto the drivers for enhanced adhesion on heavy freight hauls. At 368,000 pounds (167,000 kg) in basic empty weight, the SD50's robust six-axle setup provided superior stability and for dragging long, heavy over varied , though this contributed to higher consumption compared to four-axle contemporaries. The short hood at the front end of the body was elevated to enhance forward visibility for the , a choice inherited from prior EMD models that prioritized operational safety on mainline routes. However, the direct frame-mounted power assembly could transmit vibrations to the cab during high-load operations, potentially affecting comfort over extended runs, though this was a common trait in pre-microprocessor-era locomotives. The cab itself was a standard Spartan-type enclosure, 10 feet 3 inches (3.12 m) wide, offering basic crew accommodations without the full-width extensions seen in later safety cabs, and it predated 1990s Federal Railroad Administration crashworthiness requirements. Inside, it included an AAR-standard engineer's control stand positioned to the left of the operator's seat, featuring integrated throttle, dynamic brake, and reverser controls for intuitive handling, alongside an auxiliary seat and electric cab heaters for basic comfort. Operational safety and auxiliary features emphasized reliability in multi-locomotive consists, with multiple-unit (MU) capability allowing synchronization of up to 12 units via jumper cables for in long trains. The employed Westinghouse 26L air brake equipment for precise control, complemented by automatic sanding systems delivering sand from a 56-cubic-foot (1.6 m³) capacity reservoir to improve traction on slippery rails. Additional safeguards included slip indicators, protection, and ground fault relays, all integrated into the cab displays to alert operators to potential hazards without advanced electronic monitoring.

Variants

SD50S

The SD50S was a specialized short-frame variant of the EMD SD50 diesel-electric locomotive, designed for enhanced performance in heavy-haul freight service on routes with pronounced curves. Built to address the needs of railroads operating in challenging terrain, the SD50S utilized a modified frame derived from the earlier SD40-2 model, reducing overall length to 68 feet 10 inches and enabling better negotiation of tight radii while maintaining the core power output of the standard SD50. In late 1980, Electro-Motive Division (EMD) produced six prototype SD50S units for the Norfolk & Western Railway (N&W), numbered 6500 through 6505 and delivered in December. These locomotives weighed 368,000 pounds and were equipped with the 3,500-horsepower 16-cylinder 645F3B turbocharged prime mover, paired with six D87 traction motors for a top speed of 65 mph. Optimized for the N&W's coal-hauling operations in the Appalachian region, the shorter frame improved on steep grades by concentrating weight more effectively over the trucks, allowing for reliable pulling of heavy unit trains despite the railroad's sinuous track layout. The units were later upgraded with free-flow blower ducts in to enhance cooling efficiency. Complementing the prototypes, five additional SD50S locomotives were constructed in 1982 by EMD licensee in for Hamersley Iron, numbered 6060 to 6064. These export models retained the 3,500 hp 645F3B engine but incorporated adaptations such as Australian-standard safety couplers and other modifications for compliance with local regulations and operational requirements. Deployed on trains in Western Australia's region, the SD50S units excelled in heavy-haul duties similar to their N&W counterparts, leveraging the short-frame design for stability on undulating grades laden with multi-tonne loads. In total, only 11 SD50S locomotives were ever built. Performance across the fleet highlighted the variant's strengths in and ride quality, with crews on both continents praising the locomotives for their power delivery in demanding service. However, as newer models like the SD60 and SD70 emerged, the aging SD50S units were phased out; the Hamersley Iron fleet was retired in 1996 and exported to the for secondary use, while the N&W units transferred to Southern upon the 1982 merger and remained in service until the early 2010s before final due to accumulated mileage and .

SD50F

The EMD SD50F was a cowl-bodied variant of the SD50 diesel-electric locomotive, built exclusively for the Canadian National Railway () to provide a full-width body design suited to the railroad's operational needs. Featuring a streamlined carbody reminiscent of earlier passenger locomotives like the SD40F, the SD50F incorporated the "Draper Taper" behind the cab, named after CN's chief motive power officer William Draper, to enhance visibility and safety during operations. This design prioritized comfort in the wide-nose cab while allowing access through the engine room, though it presented challenges such as poor insulation leading to temperature extremes and the need to open doors for ventilation. Production of the SD50F occurred at General Motors Diesel Division's (GMDD) facility in London, Ontario, from April 1985 to July 1987, with a total of 60 units constructed, numbered CN 5400–5459. Powered by the EMD 16-645F3B V16 engine rated at 3,500 horsepower, the locomotive measured 71 feet 2 inches in length and weighed 368,000 pounds, with HTC trucks in a C-C configuration and a gear ratio of 62:15. Unique features included larger radiator intakes to support enhanced cooling demands, a roof-mounted dynamic brake grid, and the AR11 alternator paired with D87A traction motors for reliable performance in varied service conditions. However, like other SD50 models, the SD50F inherited electrical system issues that affected reliability across the series. The SD50F's design contributed to improved over prior EMD models through refinements in the and , while the enclosed body helped reduce engine noise, making it suitable for 's mixed freight and occasional passenger-related operations across . With a top speed of 65 mph (105 km/h), it excelled in yard switching and road freight duties, offering a continuous of 82,100 pounds at 11 mph. CN retired all SD50F units by 2009, with many scrapped or stored, though a number were exported to short-line operators such as the Dakota, Missouri Valley & Western Railroad and Montana Limestone Company for continued freight service.

SDL50

The SDL50 was a specialized export variant of the EMD SD50 diesel-electric locomotive, developed for operation in the extreme desert conditions of . A total of 31 units were produced by (EMD) in phased deliveries spanning from 1981 to 2005, making it the variant with the longest production timeline. The initial order of six locomotives (numbers 3500–3505) arrived in December 1981 under order 808047, followed by ten units (3506–3515) in December 1984 via order 838085, seven locomotives (3516–3522) between November and December 1997 under order 958646, and the final eight units (3523–3530) in July–August 2005 pursuant to order 20038550. These were exclusively supplied to the Saudi Government Railroad (SGR), later known as the (SRO). Built on the SD50 platform but rated at 3,500 horsepower from the 16-645F3B prime mover, the SDL50 incorporated key adaptations for arid environments exceeding 120°F (49°C), including extra-large air filters to combat ingestion, sealed compartments to prevent infiltration, and reinforced cooling systems for sustained reliability in high-heat operations. Extended fuel tanks provided a 4,000-gallon capacity to support extended hauls across remote routes, while -resistant traction motors enhanced durability against abrasive conditions. The locomotives were finished in a distinctive yellow for visibility and heat reflection. EMD's design emphasized these modifications to ensure robust performance for long-haul freight services on SGR's network. Optimized for heavy freight duties in Saudi Arabia's vast arid landscapes, the SDL50 demonstrated effective traction and endurance, with units routinely handling container and bulk trains over distances exceeding 500 miles. Early production batches experienced filter clogging due to intense exposure, a challenge addressed through refinements in later deliveries via improved media and maintenance protocols. As of 2025, several SDL50s remain in active service on SRO lines, underscoring their despite the demanding operational environment.

Operators

Original purchasers

The EMD SD50 and its variants were initially acquired by several major North American Class I railroads and export operators during the early , amid railroad deregulation under the , which encouraged investments in higher-horsepower locomotives for expanded freight operations. These purchases focused on road freight and heavy-haul applications, such as coal, merchandise, and general freight trains, rather than passenger service. placed the largest order, acquiring 135 SD50s between 1983 and 1986, numbered 6700–6834, primarily for Eastern freight including coal and heavy merchandise over mountainous terrain. Other significant U.S. buyers included the , which ordered 60 SD50s in late 1984, numbered 5000–5059, for heavy-haul service on its routes. The Norfolk & Western Railway purchased 6 SD50S short-frame variants in December 1980, numbered 6500–6505, dedicated to service in the Appalachian region. The followed with 15 standard SD50s in July 1984, numbered 6506–6525, also for freight duties. subsidiaries, the Chesapeake & Ohio and Baltimore & Ohio, together acquired 63 SD50s between 1984 and 1985 for general freight, while the Seaboard System bought 81 units from 1983 to 1985 in the 8500–8580 series. Smaller fleets went to the Denver & Rio Grande Western (17 units, 1984, numbered 5501–5517), Chicago & North Western (35 units, 1985, numbered 7000–7034), and Kansas City Southern (10 units, 1981, numbered 704–713).
RailroadVariantQuantityBuild YearsRoad NumbersNotes
SD501351983–19866700–6834Eastern freight, coal and merchandise over mountains; largest fleet.
Missouri PacificSD506019845000–5059Heavy-haul freight.
Norfolk & WesternSD50S619806500–6505Coal service in .
SouthernSD501519846506–6525Road freight.
Seaboard SystemSD50811983–19858500–8580General freight.
Chesapeake & OhioSD50431984–19858553–8575, 8624–8643General freight.
& OhioSD502019848576–8595General freight.
& WesternSD501719845501–5517Mountain freight.
Chicago & North WesternSD503519857000–7034Freight service.
Kansas City SouthernSD50101981704–713Road freight.
Canadian buyers centered on the Canadian National Railway, which ordered 60 SD50F cowl-body variants between 1985 and 1987, numbered 5400–5459, for mixed freight across its transcontinental network. Export orders included 5 SD50S units built in 1982 by EMD licensee for Hamersley Iron in , numbered 6060–6064, intended for haulage in the region. The Saudi Government Railroad acquired 31 narrow-gauge SDL50 variants from 1981 to 1985, numbered 3500–3530, for freight operations on its 1,067 mm gauge lines.

Subsequent operations and retirements

Following the breakup of in 1999, its fleet of 135 EMD SD50 locomotives was divided between Norfolk Southern and , with NS receiving 78 units and acquiring the remaining 57. These ex- SD50s entered service on both carriers for general freight duties across the , often in helper roles on mountainous grades and in heavy-haul trains. Norfolk Southern integrated the units into its motive power pool without major modifications initially, but reliability concerns from the SD50's 16-645F3B engine—such as frequent piston and cooling system failures—prompted progressive retirements starting in the early 2000s. CSX, meanwhile, focused on rebuilding portions of its SD50 fleet to SD50-3 specifications at its shops, addressing original design flaws like improved cooling and electronic upgrades to extend . By the mid-2010s, NS had retired nearly all of its ex-Conrail SD50s, with the final unit, NS 5424, withdrawn in 2013 amid a broader fleet modernization favoring more efficient Dash 9 and AC-traction models. Some rebuilt SD50-3s remain in service on CSX for secondary assignments as of 2025, though ongoing maintenance demands continue to lead to progressive retirements. Canadian National's 60 SD50F cowl units, delivered between 1985 and 1987, faced similar operational challenges and were fully retired between 2008 and 2009 after accumulating over 25 years of service primarily in bulk freight on the prairies. A handful were sold to regional carriers, including nine to the Dakota, Minnesota & Western Railway, where they continued in revenue service until the mid-2010s before further dispersal or storage. Union Pacific, which acquired 30 SD50s from Chicago & North Western in 1995, retired its entire fleet by 2001 due to high downtime rates and incompatibility with UP's evolving AC strategy. Surviving SD50s found extended roles on regional and short-line railroads, where lower traffic volumes offset maintenance costs. The Wheeling & Railway acquired several ex-Conrail units in the early for coal and steel traffic in and , operating them until the early 2020s when fleet replacements and emissions compliance pressures prompted withdrawals. By 2020, more than 90% of the approximately 492 SD50 and variant locomotives built worldwide had been retired, driven by their 40-plus years of age, non-compliance with modern EPA Tier standards, and the availability of higher-horsepower, lower-emission alternatives. As of November 2025, fewer than 20 SD50 variants remain in North American , mostly on short lines or in fleets, with the majority of survivors exported to international operators. In , the Saudi Railways Organization's 31 SDL50 units—export adaptations built in 1981—continue active duty hauling freight along the North-South Railway and Dammam-Riyadh line, benefiting from desert-hardened modifications and ongoing parts support.

Rebuilds and modifications

Deratings and conversions

Due to persistent reliability issues with the EMD 16-645F3B prime mover, particularly overheating and frequent engine failures stemming from its high operating speed of 950 rpm, numerous SD50 locomotives underwent programs in the and to reduce stress on the powerplant and extend . These modifications typically involved lowering output to 3,000 horsepower, aligning the units' performance with the more proven SD40-2 configuration while retaining the SD50's 2 electrical and control systems. Railroads pursued these changes to improve , cut costs, and boost overall , often through relatively straightforward adjustments like recalibration or modifications rather than full engine replacements. Norfolk Southern implemented one of the most extensive conversion efforts, rebuilding 58 SD50 and SD50S units—many inherited from , including over 20 former locomotives—into SD40E models at its Juniata Locomotive Shop between 2008 and 2013. These conversions replaced the problematic 16-645F3B engines with rebuilt 16-645E3 units rated at 3,000 horsepower, along with upgraded cooling systems and control electronics, primarily for pusher service in the Alleghenies and other helper duties. Similarly, derated its entire fleet of approximately 197 SD50s—comprising original orders from Seaboard System, , and assets—to 3,000 horsepower starting in 2006, reclassifying them as SD50-2 units to address ongoing maintenance challenges and optimize fuel consumption without major structural overhauls. Union Pacific also conducted deratings on its inherited Missouri Pacific SD50s, rebuilding around 40 of the 60-unit group to SD50M configuration beginning in mid-1994 and continuing into 1995, which reduced power from an initial 3,600 horsepower to 3,500 horsepower while enhancing cooling capacity to combat thermal issues. These programs collectively affected over 100 SD50s by 2010, transforming them into more dependable workhorses for freight service, though at the expense of their original high-horsepower advantage. The modifications generally extended operational longevity by a decade or more, with reported improvements in reliability allowing units to achieve utilization rates comparable to contemporary SD40-2s.

Modern rebuild programs

In the 2010s, CSX Transportation initiated a significant rebuild program at its Huntington Locomotive Shop in West Virginia, converting select EMD SD50 locomotives into the SD50-3 configuration to extend their service life and incorporate modern technology. These rebuilds involved a complete overhaul, including the installation of a Wabtec microprocessor control system for improved engine management, a rebuilt 16-645E3C prime mover derated to 3,000 horsepower from the original 3,500, and the Wabtec FastBrake electronic air brake system for enhanced braking performance. Additional upgrades included rebuilt electrical rotating equipment, cab modifications for crew comfort such as a new control stand with LCD display and provisions for positive train control (PTC) screens, and other enhancements to boost reliability. A total of 14 SD50s were rebuilt between 2009 and the early 2010s, with examples including CSX 8502 (ex-Seaboard System 8502), 8523, 8526, 8536, 8540, 8568, 8582, 8604, 8609, 8612, 8613, 8614, 8619, and 8662 (ex-Conrail 8662). By 2024, four of these units remained active on the CSX roster, primarily in yard and local service, demonstrating the program's success in prolonging operational viability. Parallel to CSX's efforts, undertook one of the largest modern rebuild programs for SD50s, transforming 58 units into SD40E locomotives at its Juniata Locomotive Shop in , from August 2008 to January 2014. These conversions derated the locomotives to 3,000 horsepower while integrating advanced features such as in the cab, the EM2000 microprocessor system with a new electrical cabinet and SmartStart technology for diagnostics and starting, and upgraded 16-645E3C engines compliant with EPA Tier 0+ emissions standards. Later units (NS 6350 and subsequent) received CCB26 electronic air brakes, cab signal and locomotive speed limiter (LSL) equipment for safety, and PTC readiness, while retaining core components like the AR11A , Super Series wheel slip control, and D87 traction motors rated at 90,500 pounds of starting . The rebuilt SD40Es, numbered 6300 through 6358, were assigned primarily to helper service in the Alleghenies and other mountainous territories, with early units (6300-6329) equipped for via Helperlink. This program not only addressed the original SD50's reliability issues but also ensured regulatory compliance and extended service life beyond 40 years for many units. Beyond these Class I railroad initiatives, smaller operators and leasing companies pursued targeted SD50 rebuilds in the 2010s to meet emissions requirements and support short-line operations, often incorporating certified retrofit kits for EPA compliance. Helm Leasing, for instance, facilitated upgrades on leased SD50s, including emissions control modifications to align with Tier 0+ standards, enabling continued use on regional and short-line railroads where cost-effective power was essential. Overall, these modern programs—totaling over 70 rebuilt units across major carriers—emphasized microprocessor integration, emissions retrofits, and safety enhancements, allowing SD50 derivatives to achieve up to 50 years of revenue service while reducing downtime and operational costs. As of 2025, examples of operational rebuilt SD50s include former CSX units in service with short lines like the Indiana & Ohio Railway, highlighting their adaptability in secondary markets.

Preservation

Preserved locomotives

As of 2025, the only confirmed preserved example of the EMD SD50 locomotive is Chicago & North Western 7009, highlighting the model's historical role despite its reputation for reliability issues during revenue service. Chicago & North Western 7009 was built in November 1985 by the Electro-Motive Division in LaGrange, Illinois, as one of 35 SD50s acquired by the C&NW for hauling coal trains in the Powder River Basin. After service on the C&NW until 1995, it operated on the Union Pacific as number 7009 until 2001, then was stored at National Railway Equipment in Silvis, Illinois, until its acquisition by the Illinois Railway Museum in 2022. This locomotive marks the first and only SD50 to be preserved by any museum and remains in its original Chicago & North Western paint scheme. It is currently on static display at the Illinois Railway Museum in Union, Illinois, though it has undergone startup testing and limited operational runs on museum trackage as of 2023.

Restoration and operational status

As of 2025, Chicago & North Western No. 7009, housed at the Illinois Railway Museum (IRM) in Union, Illinois, is the only preserved EMD SD50 and has undergone partial restoration. Acquired by the museum in 2022 from (NREX), the locomotive—built in November 1985 at EMD's plant—retains its original configuration with a 3,500-horsepower 16-645F3B . Restoration efforts at IRM have focused on returning the unit to serviceable condition while preserving its historical Chicago & North Western markings and features. By 2023, No. 7009 had completed its first startup since arrival and limited switch moves, but it is not yet fully operational for regular use on the museum's 5-mile demonstration railroad. This partial restoration marks a significant achievement in diesel locomotive preservation, as SD50s were largely retired from mainline service by the early 2010s due to reliability issues and fleet modernizations. No other SD50s are known to be preserved or actively restored for operational use in settings, though a small number remain in industrial or short-line service, often after rebuilds. The IRM's example stands as the sole representative in preservation, highlighting the model's transitional role in EMD's lineup.

References

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  2. http://thedieselshop.us/Data%20EMD%20SD50.HTML
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  4. https://www.athearn.com/on/demandware.static/-/Sites-athearn-us-Library/default/dwabfe2db3/announcements/july-2024/01_GENHO_SD50_062824.pdf
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  29. https://www.rrpicturearchives.net/locoList.aspx?id=UP&mid=11
  30. https://www.wvncrails.org/sd50-farewell.html
  31. https://www.rrpicturearchives.net/locoList.aspx?mid=11
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  33. https://www.trainorders.com/discussion/read.php?2,1133382
  34. http://www.altoonaworks.info/rebuilds/ns_sd40e.html
  35. https://forum.trains.com/t/ns-sd40e-rebuild-program/188130
  36. https://www.trainorders.com/discussion/read.php?2,1222858
  37. https://utahrails.net/up-diesel-roster/up-diesel-roster-73.php
  38. https://railroad.net/sd50-dash-three-sd50-3-progress-t67565.html
  39. https://www.trainorders.com/discussion/read.php?2,4212937
  40. https://www.facebook.com/groups/CSXpastandpresent/posts/2441931972674587/
  41. https://locomotive.fandom.com/wiki/Norfolk_Southern_SD40E
  42. http://www.lmoarail.com/wp-content/uploads/2017/09/2009-LMOA-Book.pdf
  43. https://www.youtube.com/watch?v=y6Ws4iQiNs0
  44. https://www.irm.org/player/cnw7009/
  45. https://www.trains.com/trn/railroads/heritage-rail/preservation/illinois-railway-museum-acquires-sd50/
  46. https://www.irm.org/in-the-news/irm-acquires-sd50/
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