How do the block or token instruments work?
In manual block working of double lines, the block instruments that connect the two signalboxes (and which dispense the tokens in the case of token systems) have to be coordinated by the signal operators at the two signalboxes. The signalbox that accepts a train into its block section must first set the Line Clear indication on the block instrument which is reflected in an indication in the block instrument of the signalbox in the rear. The signalbox in the rear cannot pull off signals allowing any trains to proceed into the next block section until such a Line Clear indication is received. When a train enters the block section, the signalbox in front sets the block instrument to Train on line. When the train passes the signalbox in front, the block instrument indication is set to Line Closed (also known as Line Normal or Line Blocked). When there are no trains expected to be approaching or occupying the block section, the normal state of affairs is for the indications on both block in
