The EMD SDP40F is a six-axle 3,000 hp (2.2 MW) C-C diesel-electric locomotive built by General Motors Electro-Motive Division from 1973–1974. EMD built 150 for Amtrak and for a brief time they formed the backbone of Amtrak's long-distance passenger fleet. A series of derailments in the mid-1970s led to their early retirement in favor of the EMD F40PH. Several were rebuilt and found a second life with the Atchison, Topeka and Santa Fe Railway in freight service.
Amtrak inherited an aging and mechanically-incompatible fleet of diesel locomotives from various private railroads on its startup in 1971. The most modern locomotives remained in private hands to operate the various commuter services which, by law, did not pass to Amtrak. The mainstays of Amtrak's road diesel fleet were veteran EMD E8s and EMD E9s, which were all 10–20 years old and due for replacement.
The design of the SDP40F was based on the EMD FP45 passenger locomotive. Both shared the EMD 645E3 diesel engine (prime mover, although the SDP40F had 16 cylinders instead of 20. The prime mover developed 3,000 hp (2.2 MW). The space saved from the smaller prime mover was given over to increased water capacity. The SDP40F had an underbody tank split between water and diesel fuel, carrying 2,000 US gallons (7,570.8 l; 1,665.3 imp gal) of water and 2,500 US gallons (9,463.5 l; 2,081.7 imp gal) of diesel. A second 1,500-US-gallon (5,678.1 l; 1,249.0 imp gal) water tank sat in the carbody, forward of the steam generators which produced the steam needed for supplying heat (and sometimes cooling) and hot water for the train.
They were full-width body cowl unit locomotives, similar in appearance to the traditional cab units that many passenger locomotives at the time featured, but featuring a normal frame and superficial bodywork, rather than having a frame integrated with the bodywork, as in a cab unit. Basically, they were identical structurally to the narrow-hood SD-40 road switcher freight locomotive, but with a "passenger-style" full width cab. One difference was that as a passenger locomotive, it featured a higher 57:20 gearing that allowed 100 mph (160 km/h). They were designed for easy conversion to freight locomotives should Amtrak cease operation.
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 cowl unit, which it named FP45 and F45. Although the SDP40F was externally nearly identical to the FP45, 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. 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.
Amtrak ordered a total of 150 SDP40Fs. Eventually, the SDP40F was phased out as all-electric cars, such as the Amfleet, displaced the old steam heat rolling stock. While the SDP40F was designed with conversion to head-end power (HEP) in mind, the bad press they received, cost to upgrade and overhaul the units, and Amtrak's satisfaction with the versatility of the HEP-equipped F40PH ultimately doomed the SDP40F. Amtrak was able to trade in the SDP40Fs to EMD as more F40PH units were acquired in the late 1970s. The last SDP40F was retired in the early 1980s.
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 the lightweight baggage cars, which caused harmonic vibrations when placed directly behind the much heavier SDP40F. Also playing a role was the sometimes poor quality of track the locomotive operated over. Some railroads hosting Amtrak trains responded to the derailments by banning the SDP40F from their rails.
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.
As Amtrak F40PHs increased in number, the SDP40F was withdrawn from service. The last revenue run of an SDP40F under Amtrak was in 1985.
In 1984, Santa Fe Railway traded lower-power locomotives to Amtrak for 18 SDP40Fs, horsepower-for-horsepower. The SDP40Fs were reconditioned in the railroad's San Bernardino, California shops to the designation SDF40-2 for use as freight locomotives. Santa Fe 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. They were also given front steps and platforms. Their noses were notched after a second maintenance shop visit in order to improve boarding access. In exchange, Amtrak received 43 smaller locomotives for use in switching service.
The last run of an SDF40-2 on took place in 2001, while being owned by the Santa Fe's successor 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. This locomotive was converted to an SDF40-2 and is currently in a Maersk Sealand paint scheme. 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.