04-08-2009, 08:21 AM
It doesn't do twice as much work. The diesel engine spins a generator which will put out max power. The maximum power the generator will put out is not determined by the number of traction motors it is powering. If you power twice as many traction motors with the same generator, you reduce the maximum speed by 1/2. Slugs are often used in yards. It seems the NS uses them in local switching as well. I don't know if they use them in mountainous territory on coal drags or not. The advantage would be more tractive effort up grades, but you trade off speed when grades level off.