The Point Speed Restriction Rail, or PSR is a rail which has a matte black texture and a strange icon drawn on it.

When given a number, it ensures that trains slow down to that speed exactly on that rail specifically. Trains then go back to their ATC-mandated speed afterwards.

When paired with ATC tracks, trains can be predictably slowed down to a required speed.

One usecase is with cargo loading/unloading tracks. The PSR can ensure trains slow to exactly 1 n/s on the track, and an ATC rail can keep the train at 1 n/s until the train has finished with its loading and unloading.

Another usecause is ATC stations, which need to have trains being able to predictably go at a specific speed at certain points of the rail.