Was steam dead by 1956?
Wyhog has it about right.
I think that if one were to get the actual figures for each USA Class 1 RR in 1956 you'd find that probably 90% of the ton-miles that year were hauled by diesels (except perhaps for a few holdouts like N&W). And the few percent of ton-miles still regularly hauled by steam was in relatively isolated pockets. So yes, by 1956 steam was essentially dead.
1954 would be a good year to pick for when steam was becoming a rare thing. By then many smaller to medium sized class 1 railroads were fully dieselized and most larger class 1s were sending steam to specific areas to make their last stands as other divisions were fully Dieselized.
The northern transcontinentals are a good example of where steam stood in 1954. The Milwaukee Road ended steam operations on the entire Pacific Extension that year. The Great Northern was donating 2-8-0s for display in local parks and sending their remaining big steam east for heavy haul iron ore service. Even the GN's 70 mile Cascade Mountain electrification would fall to diesel economics in 1956.
The Northern Pacific was the one bright spot for steam fans in the Northwest in 1954. With good heavy Mikados and supersteam Northerns, Yellowstones and Challengers combined with company owned coal mines the NP was still moving 40% of its revenue ton miles with steam power in 1954 and NP officials had no definite dieselization date in mind but thought it would not come until 1960 or later. But unforeseen events brought about an earlier end to steam. By 1957 farewell to steam excursions were being run in the Seattle area and in January 1958 the last steam locomotive ran in revenue service for the Northern Pacific in Duluth, Minesota.
What happened between 1954 and 1958? Several have already been mentioned and the 1958 recession was very significant. One 1954 event should not be overlooked, the introduction of the GP9. The assignment by the GN and NP of their last steam to heavy haul ore service gives a clue to why the GP9 was so important in putting the last nails in the coffin of steam.
The GP9 looks very similar to the GP7. Most rail fans know that the GP9 had a prime mover that could generate 1750 HP for traction, a 250 HP increase over the GP7. The GP9's 567C engines also had several maintenance saving improvements over the 567B of the F3, F7 and GP7. But perhaps more important was the improved D37 traction motor used on the GP9. With the D37 the GP9 wasn't just the most powerful single engine EMD locomotive to date, it could perform better in low speed heavy haul service than any four axle EMD locomotive that proceeded it. The NP, GN and roads like the N&W kept steam in heavy haul service in part because steam locomotives didn't overheat their traction motors at low speed like earlier diesels were prone to do.
With the GP9 EMD had a locomotive that could beat any steam locomotive ever built in cost and performance in any type of freight service. Three GP9s could out perform any Berkshire in moving fast freight. Four GP9s could out lug and out accelerate any articulated ever built. And they could do it with less fuel, less water, less maintenance and fewer maintenance facilities. Their simply was no economic or performance reason not to replace a steam locomotive with a GP9.
What's more, since so many railroads had already dieselized by 1954, diesel builders backlogs were becoming shorter. While many railroads purchased diesels from builders other than EMD in the late 1940s or early 1950s based on delivery times there was less need to do so by the mid 1950s. Railroads like the NP, PRR and N&W could buy the best and they did. That was bad news for Baldwin-Lima-Hamilton and Fairbanks-Morse. They were out of the US locomotive business before the last steam locomotives dropped their fires on class 1s.
The NP purchased 176 GP9s. With them in hand there was no longer a need for 200+ Mikados, Northerns, Yellowstones or Challengers . Or B-L-H. Or F-M.
