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[quote user="MichaelSol"][quote user="futuremodal"] [quote user="MichaelSol"] The idea of a dual-source locomotive makes little sense. EMD pitched a specific design to the Milwaukee Road in 1972, converting SD40 locomotives to alternative 3kV DC by the addition of a pantograph and related control equipment. Naturally, it cost more than either the straight Diesel or the straight Electric. This meant, when being used in the Diesel mode, it cost more per horsepower than a comparable Diesel-electric. When used in the electric mode, it cost more per horsepower than a comparable straight Electric. On 600-800 miles runs, there just wasn't a cost savings compared to simply switching motive power.[/quote]In this analysis, you're continuing to maintain two separate fleets.  But what if the dual mode locomotive allowed for a 1 for 2 replacement, aka 1 dual mode locomotive replaces 1 straight electric and 1 diesel?[/quote]Well, a locomotive can only be in one place at one time.Maybe an example.Milwaukee Train # 261 generally arrived in Harlowton at 9:45 p.m. powered by 4 SD40 locomotives, 12,000 h.p. At Harlow, a 6,000 h.p. Little Joe electric was put on. The SD40 had a 1,020 ton rating from Piedmont to Donald, the ruling grade on the run, at 18 mph. The Joe was rated at 1,440 tons at 25 mph. on that grade. The train on April 28, 1972 was limited to 50 cars, 3500 tons. The Joe was taken off at Avery and the train ran on with the Diesel engines to Tacoma arriving at 4 a.m. 31 hours later. At Avery, the Joe could be turned and run eastbound on 262 in the afternoon. Basically, it was that Joe running over the three mountain ranges on the Rocky Mountain Division that gave both 261 and 262 their fast times. Train #262 likewise left Tacoma with a four unit SD40.So, the "train cycle" for #261 and #262 involved two sets of four SD40s, eight total, and a Little Joe Electric that swung between the two trains for the Rocky Mountain Division run. The cost of the train cycle was as follows:Little Joe equivalent: $540,000SD40s @$270,000 = $2,160,000.  Total cost for the equipment cycle = $2,700,000.The dual-mode SD40s were estimated at 140% of the cost of the Diesel-electric version of the SD40, although another estimate was 180%.  Using the 140% estimate, the bad news: in diesel mode they put out 3,000 h.p.. The good news, in electric mode they generated 5,400 hp.. So, #261 would still need four of them to haul the train in Diesel-electric mode, eight for the total cycle. Cost $3,780,000. But, with four of them, at 5,400 hp in the electric mode, the train has 21,600 hp. compared to the 18,000 hp in the combined system. The extra horsepower doesn't really do that much good, but it costs $1 million more to have it there, because you still need the four locomotives to power the train where there is no trolley, but it only cost $540,000 to have it there where it was needed in the form of a Little Joe.So the cost of the combined system, to maintain the #261/262 cycle was $2,700,000, whereas the cost of of the dual mode SD40 system to achieve the same result was $3,780,000. A straight electric system would also cost $2,700,000, identical to the combined system, to obtain the necessary horsepower.Adjusting for availability, the dual mode locomotive gets dim. It would cost as follows to purchase the motive power equipment to operate #261/262 on the Harlowton/Tacoma cycle:Straight electric: $2,934,783.Combined system (Milwaukee Electrification): $3,158,385.Straight Diesel-electric (10 units, Milwaukee Dieselization): $3,214,286. It was a little higher than this as SD45s were thrown into the mix.Dual mode locomotive system: $4,973,684.Adjusting for economic service life and financing charges, the systems diverge considerably.The Power Manual in effect April, 1972 shows 4 sections of #261 operating between Harlowton and Tacoma, and 4 sections of 262. The total motive power costs are as follows:Electric: $11,739,132.Combined System: $12,633,540.Diesel-electric: $12,857,144.Dual-mode: $19,984,736.[/quote]Well, that's a good example, albeit I can see a bit of an aberation regarding the westbound Joe into Avery being the same Joe for the eastbound out of Avery.  If that's the way it was done, then so be it, but was it normal SOP for the inbound Joe at Avery on #261 to also be the outbound Joe for #262?  I take it also that the idea of an abreviated electrifiction was never studied, aka instead of keeping the electrification from Avery to Harlowtown, reduce it to Avery-Haugen/Butte-Whitehall/Ringling-Martinsdale respectively.  Again, it comes down to the cost of maintaining catenary where needed (with that 5,400 hp per unit under wire) but eliminating it where diesel mode (at 3,000 hp per unit) would suffice.That being said, would the #261/262 have needed four diesels on the flatter stretches, or could it have made it with three, knowing that when grades were approached and catenary became available, that 9,000 combined hp under diesel mode would become 16,200 hp under wire?To bring this to a contemporary example, take the MRL between Helena and Mullan Tunnel.  MRL has been running a helper district here to tackle the 2.2% westbound grade, right?  Also, operation of hard working diesels inside the tunnel is a constant problem.  I think this is an example of where a dual mode locomotive would work out best financially, since it would replace manned helpers.  Just electrify from Helena to the west portal, no need to cut helpers in and out.  Maybe do the same on Bozeman - electrify the eastbound and westbound grades, but leave the flatter sections as is.  That would allow MRL to run straight from Laurel to Spokane without any engine changes, helpers in/helpers out, or having to overpower the consists on the flats to ensure adaquate hp for the grades.  Unless and until someone invents the fully automatic unmanned DPU.......[V]Although I suspect Michael would suggest electrifying the MRL from Garrison to Livingston!
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