A heavy locomotive chassis equipped with traction motors but lacking a prime mover. It draws electrical power from a coupled mother locomotive. In yard operations, it provides massive tractive effort at the very low, continuous speeds required to push heavy cuts of cars over a classification hill without overheating the motors.
Tie the mother and hump slug onto that drag and start shoving at two miles an hour.
Unlike road slugs, hump slugs are heavily ballasted with concrete or scrap metal to maximize adhesion at a crawl.
Related terms
Slug
A heavy, motor-equipped unit without an engine that draws power from a coupled locomotive.
Mother
A fully equipped diesel-electric locomotive that provides electrical power to a semi-permanently coupled slug.
Hump yard
A classification yard where cars are pushed over a small hill and roll by gravity into sorting tracks.
Yard slug
A low-profile, unpowered locomotive chassis equipped with traction motors to provide extra pulling force in a switching yard.