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Brian, There are a couple of ways to take your question, and I will answer what I think you asked which is why does one railroad use helpers on a 2% grade but another uses them on a 1% grade. The reason has to do with the ruling grade on the rest of the territory. In the Western mountains helper grades are generally 2% or so. The ruling grade, setting aside the helper grade, will often be about half the helper grade. For example, GN Stevens Pass is 2.2% both ways with 1% on the approaches. You size the train for the speed you want on the approaches, say 1.5 HPPT but if real drag operation you could get by with 1 HPPT. Use the 250,000# drawbar rule and you could have 25,000 tons and 25,000 HP, which is much more than would typically be operated in this territory. More realistic would be 12,000 HP with a 9-10,000 ton train. That will give you a speed greater than minimum countiuous speed. And there is about 1.3 #/ton rolling and air resistance. For help need to double the power if double the grade. On a mountain railroad with 10 degree curves helper would likely be cut in to reduce in train forces. Rear helpers OK with unit trains. Now consider a line in the east with a short 1% grade on an otherwise .5% territory. Choice is to either power every train for the 1%, or power for .5% and help. Here pushers more likely as amount of power in your helper will probably be less than in the 2% case. This is the kind of territory where diesels eliminated a lot of helper operations. Most western railroads count 1% or less as flat, they just power for them. Helpers are an operational pain. The point is "it all depends", on the traffic, how fast it has to move, and on the relative costs of powering through for the steepest hill, vs under powering with helpers. I hope this answers the question you had in mind. Mac McCulloch
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