A method of operation on the main track. Yard limits are designated in the timetable and noted by signs along the track. Within yard limits trains and engines may use the main track without protecting against other trains, except they must clear the times of first class trains. Second class and inferior trains must make all movements at restricted speed. Exceptions in some rule books:
- Second class trains must also be cleared and they may also proceed at track speed.
- Trains may proceed at track speed if the track is known to be or can be seen to be clear. Clear means no obstructions and all switches lined.
- An automatic block signal system can be used to determine if the track is clear, a signal better than approach indicates the track is clear.
- The dispatcher may have to authorize a train to enter the main track in yard limits (mostly PRR or PRR derived rules).
Yard limits only apply to the main track, they do not apply to yard tracks, leads or sidings. Yardmasters do not “authorize” train movements in yard limits (unless noted in special instructions). In yard limits trains may move in either direction. If they cannot clear a first (or second) class train, they will have to provide flag protection. First (and where authorized, second) class trains may proceed at track speed. All other movements are made at restricted speed, prepared to stop short of train, engine, switch not properly lined or obstruction, not to exceed 20 mph (speed may vary by railroad).