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Amtrak 621 with the San Francisco Zephyr over the Truckee River in Verdi, Nevada, February 1975.jpg
SDP40F No. 621 leads the San Francisco Zephyr over the Truckee River at Verdi, Nevada in 1975
Type and origin
Power type Diesel-electric
Builder GM Electro-Motive Division (EMD)
Build date June 1973–August 1974
Total produced 150
AAR wheel arr. C-C
Gauge 4 ft 8 12 in (1,435 mm)
 • Truck
Length 72 ft 4 in (22.0 m)
Width 10 ft 4 in (3.1 m)
Fuel capacity 2,500 US gal (9,463.5 l; 2,081.7 imp gal)
Water cap 3,500 US gal (13,248.9 l; 2,914.4 imp gal)
Prime mover EMD 645E3
Engine type V16 diesel
Cylinders 16
Loco brake straight air, dynamic brakes
Train brakes air
Performance figures
Maximum speed 94–100 mph (151.3–160.9 km/h)
Power output 3,000 hp (2.2 MW)
Locale United States

The EMD SDP40F was 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 fleet. A series of derailments in the mid-1970s led to their early retirement in favor of the EMD F40PH. Amtrak traded most of the fleet into EMD to be rebuilt as F40PHs; the remainder were rebuilt and found a second life with the Atchison, Topeka and Santa Fe Railway in freight service. These freight units, designated EMD SDF40-2, remained in service until 2002.


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.[1]


The SDP40F was a full-width cowl unit. Visually it resembled the EMD FP45 passenger locomotive; internally it was based on the ubiquitous EMD SD40-2 freight locomotive. Both shared the EMD 645E3 diesel engine prime mover, which developed 3,000 hp (2.2 MW).[2][3] The locomotive had a gear ratio of 57:20. Maximum speed at full horsepower was 94 mph (151.3 km/h);[4] the locomotive exceeded 100 miles per hour (160.9 km/h) in tests.[5] They were designed for easy conversion to freight locomotives should Amtrak cease operation.[6]

In the early 1970s Amtrak's passenger car fleet was still steam-heated; Amtrak's requirement called for two steam generators.[7] These were located at the rear of the locomotive. Forward of the generators was a 1,350-US-gallon (5,110.3 l; 1,124.1 imp gal) water tank. Critically, this tank rested above the carbody; the lateral motion of the water within would later be implicated in a string of derailments. The primary underbody tank was split between water and diesel fuel, carrying 2,150 US gallons (8,138.6 l; 1,790.2 imp gal) of water and 2,500 US gallons (9,463.5 l; 2,081.7 imp gal) of diesel.[8][note 1] Provision was made for eventual conversion to HEP, but it was never carried out.[11]

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,[12] 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.[13] 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.[14]

There were several minor differences between the first 40 locomotives built and later examples. The most important was the installation of lower-profile cooling fans in the rear of the locomotive in order to avoid clearance problems in the Eastern United States.[15]


An EMD E8 heads up the Coast Starlight in 1974. Amtrak planned to replace its aging E-units with the EMD SDP40F
An EMD F40PHR, rebuilt from an SDP40F, with an SDP40F on the head of the Southwest Limited 1981. The SDP40Fs time with Amtrak was drawing to a close

Amtrak ordered a total of 150 SDP40Fs, in two batches. The first order, placed on November 2, 1972, was for 40 locomotives, at a cost of $18 million. A second order, for 110 locomotives at $50 million, followed on October 12, 1973.[16] Amtrak deployed the original 40 locomotives on Western long-distance trains. The first locomotives entered revenue service on June 22, 1973, hauling the Super Chief from Chicago to Los Angeles over the tracks of the Atchison, Topeka and Santa Fe Railway. SDP40Fs were also used on the Burlington Northern Railroad.[17] The arrival of the second order enabled Amtrak to deploy the SDP40Fs throughout the country, displacing the inherited E-units.[18] In late 1975 J. David Ingles called them the "stars of Amtrak's long-distance trains."[19]


This happy state of affairs did not persist. Operating crews reported that the locomotives rode poorly compared to the E-units they had replaced.[20] Even as Amtrak and EMD investigated the ride quality, the SDP40F was involved in a series of derailments which would culminate in an abrupt end to its career as a passenger locomotive. Between 1974–1976 the Federal Railroad Administration identified thirteen separate incidents for which the locomotive was responsible.[5] 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 and created too much lateral motion.[21] 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.[22] A contributing factor was the sometimes poor quality of track the locomotive operated over.[23]

Amtrak took several corrective measures, including speed restrictions on curves and emptying the smaller of the two water tanks in order to reduce lateral motion.[24][5] The measures helped, but the trouble continued. Several railroads, including the Burlington and the Chesapeake and Ohio Railway (C&O), banned the "rail breakers" from their tracks.[25] Another important development was the unusually harsh winter of 1976–1977, which sidelined many of Amtrak's aging steam-heated coaches. Amtrak suspended numerous routes and pressed the new HEP-equipped Amfleet I coaches, designed for short runs, into service. The new EMD F40PH, intended for short-distance service and equipped with HEP, handled these trains.[26]

In the spring of 1977 Amtrak decided to abandon the SDP40F in favor of the F40PH. Amtrak traded 40 SDP40Fs back to EMD; components including the prime mover were installed into an F40PH's frame.[27] Between 1977–1987 Amtrak would trade 132 of the SDP40Fs back to EMD for F40PHRs. The SDP40F remained in service on the Santa Fe longer than anywhere else, although the arrival of HEP-equipped Superliner cars on the Western routes displaced them from there as well. The last SDP40Fs left the Amtrak roster in 1987.[28]

Freight use[edit]

Santa Fe SDF40-2 No. 5261 in California in the late 1980s.

In 1984 Amtrak, low on light-duty power, traded 18 SDP40Fs to the Santa Fe for 25 CF7s and 18 SSB1200s. Santa Fe rebuilt the locomotives for freight use. Modifications included removing the steam generators and regearing for lower speed.[29] The locomotives were also given front steps and platforms, and notched in order to improve boarding access. The rebuilt locomotives were designated SDF40-2.[30]

The SDF40-2s continued in service with the BNSF Railway, successor to the Santa Fe, until their retirement in 2002.[31] One, ex-Amtrak No. 644, was acquired by Dynamic Rail Preservation Inc. and is on display in Ogden, Utah.[32]


  1. ^ Sources agree on a 6,000-US-gallon (22,712.5 l; 4,996.0 imp gal) total tank capacity and 3,500-US-gallon (13,248.9 l; 2,914.4 imp gal) water capacity, but some give a higher figure of 1,500 US gallons (5,678.1 l; 1,249.0 imp gal) for the carbody tank.[9][10][5]


  1. ^ Holland 2009, p. 57
  2. ^ Pinkepank 1973, p. 125
  3. ^ McDonnell 2015, p. 155
  4. ^ NTSB 1976, p. 19
  5. ^ a b c d Cook 1991b, p. 44
  6. ^ Solomon 2000, p. 162
  7. ^ Ingles 1975, p. 25
  8. ^ Cook 1991a, p. 64
  9. ^ Holland 2009, p. 58
  10. ^ NTSB 1976, p. 17
  11. ^ Cook 1991b, p. 47
  12. ^ McDonnell 2015, pp. 154–155
  13. ^ Graham-White 2002, pp. 97–98
  14. ^ McDonnell 2015, p. 156
  15. ^ Cook 1991b, p. 42
  16. ^ Congress 1974, p. 41
  17. ^ Cook 1991b, p. 42
  18. ^ Ingles 1975, pp. 26–27
  19. ^ Ingles 1975, p. 24
  20. ^ Cook 1991b, pp. 43-44
  21. ^ McDonnell 2015, p. 155
  22. ^ Graham-White 2002, pp. 105; 107
  23. ^ Sanders 2006, p. 126
  24. ^ Holland 2009, p. 58
  25. ^ Cook 1991b, p. 46
  26. ^ Graham-White & Weil 1999, p. 56
  27. ^ Cook 1991b, p. 49
  28. ^ Cook 1991b, p. 50
  29. ^ Danneman 1986, p. 52
  30. ^ Foster 1996, p. 88
  31. ^ Lustig 2003, p. 29
  32. ^ Franz, Justin (May 22, 2014). "With the torches fired up, railfans hope to save F45 in the eleventh hour". Trains News Wire. Retrieved April 2, 2017.  (subscription required)


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