The state of tension throughout a train when the locomotive is pulling and the slack between the cars is fully stretched out. Engineers must carefully manage this force, especially over undulating terrain, to prevent breaking a knuckle or tearing out a drawbar. A train is said to be in draft when the pulling forces exceed the braking or rolling resistance forces.
Keep the train in draft as you crest the hill so the rear end doesn't run in and knock you around.
Managing the transition between draft (stretched) and buff (bunched) is the core skill of a freight engineer.
Related terms
Slack
The free play in couplers and draft gear that lets cars move a little toward or away from each other.
Drawbar
A solid metal beam or assembly that connects railcars or locomotives together to transmit pulling force.
Knuckle
The hinged, hook-shaped part of a railcar coupler that closes and locks to join two cars.
Pull-apart
A break in the rail, usually at a joint or weld, caused by the rail shrinking in extreme cold.