The problems many railroads had with Amtrak's SDP-40F's had much to do with their track structure & maintenance levels, and less to do with the units themselves. While BN & Chessie were restricting the units' speed on curves, Santa Fe & Union Pacific were regularly running them @ 90 MPH and they stayed on their tracks just fine. Some railroads blamed the units' extra water tanks inside the carbody as being the reason; however when Amtrak stopped filling these water tanks the units still jumped the tracks. Then the HT-C truck with its' unique, Amtrak - only hollow bolster was implicated. After extensive tests by the FRA and DOT Pueblo folks, it was determined that the lightly loaded baggage car behind the units was the first to derail, with the tightlock couplers then pulling the SDP's off the track also. Placing a heavier deadhead coach or sleeper directly behind the power solved the problem. By then it was too late for the SDP's, as the freight RR's soured on them & Amtrak decided to trade them in on F - 40's. The fact that Santa Fe traded a bunch of their decrepit switchers for a number of Amtrak SDP's was a good indicator of their faith in the units. Of course SFe removed the steam generators, as they were unnecessary in freight service. However, Santa Fe did modify the underframe tanks to all - fuel, with no adverse affects.