Ballast spreads the load from the ties into the roadbed, locks the ties against shifting sideways and lengthwise, and lets rainwater drain quickly. Main lines use hard, angular crushed stone such as granite or trap rock, because rounded gravel rolls under load. Ballast fouled with dirt or coal dust stops draining and pumps mud, so the track has to be undercut or cleaned to recover.
Ballast is fouled solid through that cut, every train pumps mud up between the ties, and we've got a slow order on it again.
Track people talk about the ballast shoulder, the extra rock past the tie ends that keeps welded rail from buckling sideways.
Also heard as
- rock
- stone
- track ballast
Related terms
Tie
One of the crosswise beams that hold the rails to gauge and spread their load into the ballast.
MOW
Maintenance of way: the department and crews that build and maintain track, bridges and roadbed.
Slow order
A temporary speed restriction on a stretch of track because of its condition, heat or work in progress.
Sun kink
A sideways buckle in welded rail caused by heat, which can throw the track out of line under a train.