6. Ballast Regulators
Ballast regulation is an important maintenance task for keeping subway cars running smoothly. Ballast is found below and between track tiles. It serves many purposes including facilitating water drainage, prohibiting plant growth, helping to absorb the load and vibration of the trains, and keeping the tracks in place.
Most subway tracks no longer have ballast, but where it does exist (on outdoor above-ground stretches of track), it needs to be kept in order. Ballast regulator trains help to distribute and even out ballast on the tracks.