EMD SD80ACe - Trains Magazine

Well, tractive effort is depending on weight on driver wheels (and adhesion factor), not horsepower per se.

If you can, compare tractive effort curves from the same locomotive platform but with different horsepower. You will note that, up to the 'critical speed' (which is weight-limited) the performance is the same, but the curve that falls slowly (and which is horsepower-dependent) is moved to the right.

F=m*a is the whole story after the critical speed.

And 'horsepower talks' if you are not doing a coal drag but you want to have a fluid railroad, since you can keep the same speed with fewer locomotives (you can have two 6000hp locomotives instead of three 4300hp ones). Obviously, European electrics are different beasts, but I would like to see the incoming Amtrak 6.4MW boxes pulling fast freights as an experiment.

For USA locomotives, the practical limit is either a 20-cylinder 710G motor (around 5500hp) or a pair of medium speed diesels like the Caterpillar C175 or the MTU R4000 with automatic start-stop for better fuel economy (you keep only the one diesel for switching or idling).

Cheers,

N.F.