An uncontrolled movement of rolling stock, typically caused by a failure of the air brake system, a loss of dynamic braking on a steep grade, or cars rolling free from a yard. Runaways gain dangerous momentum due to massive weight and low rolling resistance. Crews must sometimes intentionally derail the equipment to prevent catastrophic collisions in populated areas.
Dispatch, emergency, we've a runaway train rolling east past milepost 42, no air, no dynamic.
The nightmare scenario for any hogger, often resulting from depleted brake pipe pressure on a descending grade.
Related terms
Derail
A device on a rail that lifts a rolling car's wheels off the track before it can reach another track.
Dynamic braking
Retarding force made by turning a locomotive's traction motors into generators and burning the energy off as heat.
Brake pipe
The air line running the full length of a train that charges and controls every car's brakes.