GUIDETO REGULATIONS

摘要

ABSOLUTE BLOCK: This is the basis of all current signalling systems. It is the rule whereby only one train is allowed on a stretch of line at a time - drummed into generations of signalman as "1 train, 1 line, 1 time". A traditional Absolute Block section runs from one signalbox to the next. TRACK CIRCUIT BLOCK: This is a development of the above and uses track circuits to continually show the position of a train. Sections of track are insulated from the next section, each having a small current flowing through it, and when a train enters the section, the current is 'short circuited' through the axles of the train. This lights up an indication in the signalbox on a track diagram. When the train moves off the section, the 'short circuit' is removed and the display is no longer illuminated. Under this system, a 'section' can stretch from one signal to the next, rather than between signalboxes. On single-track lines, a train is 'offered' on the block bell in the traditional sense, then 'accepted'by the signaller ahead reversing (pulling) a lever to unlock the section signal of the'box in rear. Once that is done, no other train can be accepted until the train has arrived at the'box ahead and the acceptance lever rstored to normal.