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Ashton Junction
how it works
construction
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Consider a section of double track railway line, for that is what my simulator
recreates. The most basic function of the signalling system is to keep the trains
apart - i.e. to stop one running into the back of another.
Traditionally, this was done by using signal boxes (also called
block posts
) to divide the line into
block sections.
The block section extends from the last stop signal controlled by one signal box to
the first stop signal controlled by the next
signal box. So it is a sort of 'no-man's land' between boxes.
The
Absolute Block
system provides the means of passing a train from one signal box to the next. The
object of absolute block is very simple: that
only one train shall be in the block section at once.
The system is implemented using stroke bells (for communication) and
block instruments
(sometimes these are combined into a single unit - as in the examples at right).
The block instruments indicate
the state of the section:
normal
(sometimes called line blocked, or line closed: no train in section and no train
signalled),
line clear
(permission given for train to enter section) or
train on line
(train in section). The indication is set at the box in advance (where
the train is going) and electrically repeated at the box in rear (where the train enters the section).
Absolute Block is still in use, although now mostly confined to
secondary routes. If you want to know more, then you are strongly
recommended to visit www.signalbox.org. Just be careful - with details
of signals, block regulations, an excellent photo gallery and even a monthly quiz,
you could spend hours here!
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A mini block shelf simulator! The ex-LNWR block instruments are from Sale on the
former Manchester South Junction and Altrincham Railway (now part of Metrolink);
they survived in use until 1971.
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