Derailments
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 mediocre condition of much of the track on which the SDP40F ran.
Whatever the derailment cause, the speed restrictions, along with electrification of Amtrak's passenger car fleet, led Amtrak to adopt the EMD F40PH as the standard model, based on the proven GP40-2 freight locomotive.
Santa Fe traded lower-power locomotives to Amtrak for SDP40Fs, horsepower-for-horsepower. They replaced the hollow bolsters with conventional HT-C bolsters, removed the water tanks (replacing these with concrete ballast) and used the engines on freight trains.
Read more about this topic: EMD SDP40F