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[Anonymous]

Which locomotive would be better for passenger service, a geeP locomotive or an "SD" (example: SD40-2) locomotive, and why?

[joseph2]

The GP type would be better,smoother ride.Amtrak had SDP40's in the early 1970's but rebuilt them into F40's.Once an Amtrak derailment was caused by the rough riding qualities of a SDP40.The Southern Pacific seemed to have good luck with the Fairbanks Morse six axle Trainmasters in commutor service though. Joe G.

[M636C]

It all depends on what you want your passenger train to do, but in general a GP would be better than an SD. At speed, the additional tractive effort of the two extra motors is not needed, and the speed is governed by the voltage across the motor. So for a given gear ratio the GP could do the job using less power, because it only has to produce the high voltage required for the speed for four motors rather than six, and is producing two thirds of the current required by the SD. Power is equal to voltage multiplied by current, so with two thirds of the current, you can do the job with two thirds of the power and hence fuel.

This is of course a simplified explanation, and with heavy trains stopping often, there might be an advantage in having a six motor locomotive.But in general, even big passenger trains are light by freight standards, and it is freight that six motor locomotives are usually designed for.

In Washington DC, many of the passenger locomotives are rebuilt GP40 locomotives, with addded HEP generators. They could have used SD40s to convert to passenger service, but they chose GP type locomotives, for the reasons I've outlined above.

Peter

[ndbprr]

Well I agree and disagree with what has been posted. Namely because both E and F units were used in passenger service. Six wheel trucks give a smoother ride but four wheel trucks give more weight on the drive wheels. What someone will point out is that e units had an idler axle and were still four wheel drive even though they had three axles in each truck. The SDP40's were built in the event Amtrak failed the government could sell them to the railroads as they were basically SD40's with carbodies so SD's could be used. Since passenger trains rarely ever exceed a locomotives tonnage capacity it is rather a moot point to consider and I could argue that for high speed continuous running I would want the smoother ride if I were the engineer.

[randybc2003]

Make note of the fact that the designation "SDP-40", etc., translates "Special Design PASSENGER - (model)40". A loco w/ the notation "P" in the spec. means that it had special "steam generator" to supply steam heat to the passenger cars. Nowdays, I think AMTRACK has mostly ended steam heat, and gone to "Head End Power", or HEP. This is ELECTRICITY.

Actually, I am toying w/ the idea of bashing a SDP-45. Because I want one.