And the sand made a huge difference. We had an old Elco where I worked. We used it to load slate sulphur into rail cars, 50 cars in a string. 150 tons per car. We would get stuck in the switches if we weren't carefull. Put a little sand down and off we went.
I watched a hogshead lay down a little sand and push 6000 tons of loaded cars 10 feet down the line. Brakes where all locked. Wheels just skidding. Big power, big traction.
The newer loco's use air to push (actually syphon) sand while the old steam loco's used steam.