EMD SD50 series official thread (covers all variations)

[Engineer Spike]

OK that was a bad example, but Santa Fe seemed to be pleased with the FP45.

[Allen Hazen]

Engineer Spike--
Re: "but Santa Fe seemed to be pleased with the FP45"

Then again, the Santa Fe was one of the railroads that DIDN'T impose a speed restriction on Amtrak's SDP40F units after their derailments. I think the Santa Fe, at least on their main line, had SUPER-good track: maybe they felt that because of this they could tolerate locomotives that other railroads thought might damage either themselves or the track if operated at high speeds. (I'm guessing, though.)

[Engineer Spike]

Alan, there have been other 6 axle passenger units which have been successful, such as EL/NJT U34, and the P30CH. Between my example of the FP45, and SDP40F, it still begs a few questions. One would be the wheelbase of the Flexicoil, vs. HT-C truck. Was the hollow bolster an issue? How about the above board water tanks? One theory was that sloshing water made them unstable.

I forgot to mention the SDP35, 40, and 45. I haven't heard of Seaboard, Southern Pacific, Union Pacific, nor GN/BN having any issue with them.