EMD SDP40F

Amtrak, which had begun operating most intercity passenger rail service in the United States on May 1, 1971, inherited a collection of aging and mechanically diverse diesel locomotives from the private railroads that had previously run those routes. These inherited units, including veteran E8s, E9s, and FP7s, ranged in age from roughly seven to more than twenty years old and were badly in need of replacement. To address this, Amtrak placed its first order for new-build locomotives with General Motors Electro-Motive Division on November 2, 1972, contracting for 40 SDP40Fs at a cost of approximately 18 million dollars. A second order for 110 additional units followed on October 12, 1973, at a cost of roughly 50 million dollars, bringing the total fleet to 150 locomotives. The first examples entered revenue service on June 22, 1973, when they took over the Super Chief running between Chicago and Los Angeles over the tracks of the Atchison, Topeka and Santa Fe Railway. For a time the SDP40F represented the backbone of Amtrak's long-distance passenger operations across the country. The locomotive's career was cut short by a troubling series of derailments that occurred between 1974 and 1976. The Federal Railroad Administration identified thirteen incidents attributable to the SDP40F during that period, and although none caused catastrophic casualties, their frequency alarmed both Amtrak and the railroad industry. Investigations conducted by EMD, Amtrak, the Association of American Railroads, and the FRA pointed to several possible contributing factors, including the design of the trucks, excessive lateral motion caused by the weight and movement of water in the rear-mounted tanks, and the harmonic vibrations induced by lightweight baggage cars trailing directly behind the heavy locomotives. Several railroads, among them the Burlington and the Chesapeake and Ohio Railway, banned the SDP40F from their tracks entirely. Amtrak attempted remedial measures including speed reductions on curves and draining the smaller water tank to reduce lateral sloshing, but the problems persisted. By the spring of 1977 Amtrak had lost confidence in the SDP40F and decided to retire the type in favor of the EMD F40PH, a four-axle locomotive already proving itself on shorter-distance routes. Amtrak negotiated a trade with EMD under which the majority of the SDP40F fleet was returned to the manufacturer, with components from those locomotives incorporated into new F40PHs. The remaining units were traded to the Atchison, Topeka and Santa Fe Railway, which rebuilt them for freight service and reclassified them as the SDF40-2. The Santa Fe's successor, the Burlington Northern Santa Fe Railway, continued to operate these rebuilt locomotives until retiring them in 2002. One example survives in preservation, the former Amtrak unit numbered 644.

The SDP40F was a full-width cowl unit riding on a Co-Co wheel arrangement, meaning it used two three-axle trucks for a total of six powered axles. Power came from the EMD 645E3 prime mover, a two-stroke diesel engine producing 3,000 horsepower, the same powerplant used in the contemporaneous SD40-2 freight locomotive and the earlier FP45 passenger unit on which the SDP40F's external design was closely based. The locomotive was geared with a 57:20 ratio, allowing a maximum speed at full horsepower of 94 miles per hour, and it reportedly exceeded 100 miles per hour during testing. To serve Amtrak's steam-heated passenger car fleet, the SDP40F carried two steam generators positioned at the rear of the carbody, forward of which sat an elevated 1,350-gallon water tank whose placement above the floor line and susceptibility to lateral sloshing later drew scrutiny in derailment investigations. Additional fuel and water were carried in underbody tanks, with approximately 2,500 gallons of diesel fuel and 2,150 gallons of water stored there. The design incorporated several practical concessions to uncertain circumstances. Because doubts existed in the early 1970s about Amtrak's long-term financial survival, the SDP40F was engineered to be convertible to freight service without extensive rebuilding. Provision was also made within the design for eventual conversion to head-end electrical power, though this modification was never actually carried out on any unit. The first 40 locomotives differed in minor respects from the subsequent 110, most notably in having higher-profile cooling fans and air horns that later proved problematic in the more restricted clearance environments of the eastern United States. Those later units received lower-profile versions of both components. The locomotive was fitted with a Leslie Controls SL4T air horn as standard equipment.

Models by: Athearn