The Point Speed Restriction Rail, or PSR is a special purpose track which has visible track equipment with a matte black texture and the letters TSR written 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. The menu looks like this:

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

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

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

The lettering TSR is (presumed) short for Track Speed Restriction, which is not accurate since the PSR only applies the restriction for the specific point it is located, but the PSR predates the speed limiting signs. The letters are flipped on the track equipment box on one side due to the same area of the texture being reused.