Traction truck
A traction truck , also known as a slug , is a vehicle for train operations that is occasionally used by US railroad companies . In principle, it is a greatly simplified locomotive that consists only of the bridge frame resting on the motor bogies with the traction motors with the necessary switching directions and couplings at the ends. In some cases, ballast is also placed on the vehicle frame in order to increase the pulling force through high friction weight .
In contrast to regular locomotives with a driver's cab (“A-unit”) or simply “B-unit” machines without a driver's cab, the traction truck lacks the primary energy converter in the form of a diesel engine with a generator . The electrical energy for the traction motors is obtained from the coupled normal diesel-electric locomotive , known as the "Mother", via cable connections.
The use of such traction trucks makes sense if high tractive forces are required at low speeds, since in this case the full traction power of the "mother" locomotive cannot be used alone because of the usable static friction.