UP & Double Diesels

[dldance]

there are operational limits as to how many locomotives can be used at the head end of a train. UP is frequently at that limit on Sherman Hill and Echo Canyon. I have seen two trains with 8 engines in the last 3 months. The "double diesels" were one approach to addressing their horsepower needs. The 8500 series 6000 hp units were another approach. I am wondering that with the improved reliability of today's locomotive, a double engined unit might again be practical.

dd

[Anonymous]

I suspect it was because they needed the horsepower. UP had been buying GP B-units, including GP9B's and GP30B's and running long strings of GP's on fast freights. The DD35 was essentially a GP35 A and B unit on a single frame - same number of traction motors per prime mover. The Centenials were the first single unit diesels to match the horsepower of a Big Boy so that much horsepower in a single unit wasn't new to UP. Even with that much power, Centenials often ran in pairs with a fast SD40 in between. The U50's were 'recycled' by GE from the early gas turbines.

[beaulieu]

The idea was that certain operating costs are based on the number of locomotives needed rather than how many engines each locomotive has. ( i.e. only one brakestand, two less trucks, only one cab, etc.). It turned out that the complexity and operational inflexibility costs outweighed the savings. Only the Espee followed the UP, because you needed First Class trackage to handle the very heavy locomotives. Many railroads could have operated the double-diesels over some parts of their systems, but only the UP could operate them over most of their mainlines. Especially in the timeframe when these locomotives operated. For many railroads this was a time of deferred maintenance.

[Murphy Siding]

What exactly did Union Pacific gain by buying the "double diesel" engines, such as EMD DDA35, ALCO C855, and GE U-50? (Forgive me, I pulled model numbers from memory.) Was there really anything to gain from ordering semi-custom units, that couldn't be accomplished by just buying "off the shelf " models, and hooking 2 of them together? It seems that if it was such a great idea other railroads besides Southern Pacific, would have bought into the idea too?