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AMTK 629 with 5 Emi gap Feb 1978xRP - Flickr - drewj1946.jpg
An SDP40F leads the San Francisco Zephyr west at Emigrant Gap in 1978
Type and origin
Power type Diesel-electric
Builder General Motors Electro-Motive Division (EMD)
Model SDP40F
Build date June 1973 – August 1974
Total produced 150
AAR wheel arr. C-C
Gauge 4 ft 8 12 in (1,435 mm)
Length 72 ft 4 in (22.05 m)
Width 10 ft 4 in (3.15 m)
Prime mover EMD 645E3
Engine type V16 Diesel
Cylinders 16
Performance figures
Maximum speed 100 mph (160 km/h)
Power output 3,000 hp (2,240 kW)
Locomotive brake straight air, dynamic brakes
Train brakes air
Locale United States

The SDP40F was a 6-axle diesel-electric locomotive built by General Motors Electro-Motive Division in 1973-74 for Amtrak. It had an EMD 645E3 16-cylinder turbocharged Diesel engine that generated 3,000 hp (2,240 kW).


The SDP40F was the first locomotive built new for Amtrak. Until then, most of Amtrak's engines were EMD E-units and F-units that predecessor railroads had used for many years without good maintenance, resulting in breakdowns. A modern locomotive, like the SDP40F was an interim solution.

Based on EMD's ubiquitous SD40-2 freight locomotive, 150 SDP40Fs were built over a period of two years. They had a full-width carbody many passenger locomotives at the time featured, instead of the standard narrow long hood of freight units, and included a 57:20 gearing that allowed 100 mph (160 km/h). Two Vapor steam generators and a 1,350 US gal (1,124 imp gal; 5,110 L) water tank at the rear of the engine room made the steam needed for supplying heat (and sometimes cooling) and hot water for the train, as most of Amtrak's passenger cars were steam-heated at the time. (Another tank below the frame carried 2150 gallons more water.) They were designed for easy conversion to freight locomotives should Amtrak cease operation.[1]

EMD based the SDP40F name on the existing SDP40. Several years earlier, EMD had made similar versions of the SDP45 and SD45 in a full-width carbody, which it named FP45 and F45. Although the SDP40F was externally nearly identical to the FP45,[2] EMD chose not to give the new locomotive a similar name such as FP40. EMD wanted to avoid adding a new locomotive type to their catalog due to price controls in effect in the early 1970s.[3] The following year, the F40C name was used for a similar locomotive ordered by the Milwaukee Road, equipped with head end power instead of steam generators.[2]

Eventually, the SDP40F was phased out as all-electric cars, such as Amfleet, displaced the old steam heat rolling stock. While the SDP40F was designed with conversion to HEP in mind, the bad press they received, cost to upgrade and overhaul the units, and Amtrak's satisfaction with the versatility of the head end power-equipped F40PH ultimately doomed the SDP40F. Amtrak was able to trade in SDP40Fs to EMD as more F40PH units were acquired in the late 70's. The last SDP was retired in the early 80's.


The SDP40F was mechanically reliable but experienced several high speed derailments, causing the railroads over which Amtrak ran to impose speed limits starting in 1976-77. Although the "hollow bolster" truck design was suspected, this was never proved, despite extensive investigation by EMD, Amtrak and the Federal Railroad Administration. It was supposed that the steam generators and water tank may have made the rear of the engine too heavy. Later FRA investigations concluded that the actual culprits were lightweight baggage cars on most trains, which caused harmonic vibrations when placed directly behind the much heavier SDP40F.[4] Also playing a role was the sometimes poor quality of track the locomotive operated over.[5]:126

Whatever the derailment cause, the speed restrictions, along with electrification of Amtrak's passenger car fleet, led Amtrak to adopt the EMD F40PH as their standard passenger locomotive, which was based on the proven GP40-2 freight locomotive.

In 1984, Santa Fe Railway traded lower-power locomotives to Amtrak for SDP40Fs, reconditioned under the name SDF40-2 for use as freight locomotives. They replaced the hollow HT-C bolsters with conventional HT-C bolsters, converted the below-frame combination fuel/water tank to an all-fuel tank, removed the above-frame water tanks (replacing these with concrete ballast) and used the engines for nearly 15 years. In exchange, Amtrak received 43 smaller locomotives for use in switching service.[5]:133


Santa Fe 5261, an SDF40-2, working in a freight train in California in the late 1980s.

As Amtrak F40PHs increased in number, the SDP40F was withdrawn from service. The last revenue run of an SDP40F under Amtrak was in 1985.

The last run of an SDF40-2 on took place in 2001, while being owned by BNSF Railway (then-Burlington Northern Santa fe). All units were retired in 2002, and most were scrapped in Topeka, Kansas between 2002 and 2004.


One locomotive of the type, former Amtrak 644, is owned by Dynamic Rail Preservation Inc. and is on display in Ogden, Utah. The group plans to restore it to its Amtrak as-delivered state, minus the steam generators and few other details. Amtrak now has an ACS-64 numbered 644.

Two heavily modified SDP40Fs (ex-Amtrak 509, 609) in an EMD scheme exist as test beds at Transportation Technology Center, Inc.'s test facility near Pueblo, Colorado. It is unknown what their internal configuration is, or what the future holds for them. Amtrak now has a Dash 8-32BWH numbered 509, and also now has an ACS-64 numbered 609.


  1. ^ Brian Solomon (2000). The American Diesel Locomotive. Voyageur Press. p. 162. ISBN 1610606051. 
  2. ^ a b McDonnell, Greg (2002). Field Guide to Modern Diesel Locomotives. Waukesha, WI: Kalmbach Publishing Co. pp. 142–144. ISBN 0-89024-607-6. 
  3. ^ Graham-White, Sean (2002). Electro-Motive Division's Classic Cowl Units. La Mirada, CA: Four Way West Publications. pp. 97–98. ISBN 1-885614-53-5. 
  4. ^ Graham-White 2002, p. 105,107
  5. ^ a b Sanders, Craig (2006). Amtrak in the Heartland. Bloomington, IN: Indiana University Press. ISBN 0-253-34705-X. OCLC 61499942. 


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