Remember Road Slugs? At one time CSX had a couple hundred of the things. A GP40-2 provided the traction amps for the paired slug's traction motors, an old GP30 or GP35 stripped of internals and filled with concrete.
I took this pic early '98 or '99 a couple miles up the hill towards Sand Patch from Meyersdale, Pa. See the primer-gray GP30 with no radiator vents? That is the slug. You got double the tractive effort without engines to be maintained.