Track Circuit Block, commonly abbreviated to TCB, is a method of working between signalboxes and within a box's control area.
TCB relies upon an area's running lines being track circuited throughout, thus giving proof of whether or not a section is occupied. Signals will clear provided that the section to the next signal, and an overlap beyond it, are clear. There is no general requirement for signallers at adjacent boxes to communicate with each other to allow trains to pass between them, though slots are provided when the line between them is single track or obtaining a clear overlap at the next box requires that box to take certain actions. TCB permits a single signalbox to control large and complex areas, with no need for the signaller to observe the trains themselves.
TCB has steadily replaced Absolute Block , and can be assumed to be the default working across SimSig simulations- any instances of AB will be noted in simulation manuals.
Last edited by Steamer on 11/04/2021 at 18:31