signal box simulator (in plain English)



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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 Just be careful - with details of signals, block regulations, an excellent photo gallery and even a monthly quiz, you could spend hours here!


    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.