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A slot is a 'permission' or consent for a route to be set, usually between adjacent panels or boxes, or into yards or sidings. It may be there for safety, for example a yard shunter not realising there is an incoming train, or for regulation, such as on single track lines where each end is controlled by a different panel or signalbox where one end "owns" the whole line. To 'give/grant' a slot means to give permission for a train to come to you, to 'ask for/recieve' a slot means to reqest permission to send a train away from you.

Slots, releases, and acceptances are generally called slots in SimSig for simplicity. Technically there is a difference, but as there are regional variations on naming and usage, such difference can be avoided for simplicity.

Slots work in two ways:

  • By preventing a route from setting until the slot has been given
  • By allowing routes to be set, but preventing the signal from clearing (showing a proceed aspect) until the slot has been given

They can have the following features:

  • Persistent slots stay in the "given" state until cancelled. That is, they can allow several trains to proceed without the signaller granting the slot for each train. The signaller needs to manually cancel the slot when required.
  • Non-persistent slots allow a single train to pass, and then cancel automatically.
  • Each slot has a "giver" and a "receiver". It all depends on the situation as to whether the signaller on a particular panel is a giver or receiver.
  • Some slots are requested by telephone. Thus, the signaller has to phone (for example) the depot, and the depot will advise which depot arrival road to send the train into, where there is more than one.
  • Some requestor slots cause one of a choice of slots to be granted. For example, Saltley presses a button to ask Birmingham New Street for a route, but not a specific route. Birmingham New Street responds by pressing one of two buttons, telling Saltley which route to set.

Last edited by GeoffM on 15/09/2016 at 03:00