All locomotives now have sanders (can be disabled in a loco's .json). The capacity of the sand hopper is defined in the .json and locos consume sand at a rate 1 block/5 sec when sanders are active. When active, the locomotive's traction is increased by 33%. Sanders also require steam pressure to activate. (Not on diesels obv)

Generally useful on rail lines with steep grades, when operating trains in the rain or just for accelerating quicker.