Designing Interlocking

Designing Interlocking

Signal box diagrams are relatively easy to get hold of(there are literally hundreds in print), however interlocking tables are harder to find. Therefore I have put together a few rules to follow when designing your lever frame locking tables.

Only Points & fpl use Reverse to Normal Locking - no one is going to stop you putting back a signal!

• Distant signals - only interlocked N→R (Normal to reverse). All stop signals in the block section ahead must be cleared to unlock.
• Stop signals - only interlocked N→R. If there are different signals for different routes, correct route must be set. There must be no conflicting signals cleared, e.g. different routes or bi-directional routes. Facing Point locks must be locked if applicable.
• Disc(Shunting signals) - only interlocked N→R. If disc signal only applies to some routes, correct route must be set. There must be no conflicting signals cleared, e.g. different routes or bi-directional routes. Facing Point locks must be locked if applicable.
• Points - interlocked N→R & R→N. All signals clearing trains over points in the facing direction must be on(not cleared). There must be no conflicting points set(e.g. some crossovers must be operated in a particular order). In some boxes trailing points cannot be moved if they are in the rear of a cleared signal.
• fpl - interlocked N→R. (Locked-unlocked) You can lock fpl’s anytime , it is unlocking that is interlocked! All signals clearing trains over points must be on(not cleared). In some boxes fpl’s stand out, so are reversed when locked. In this case the locking would be R→N.

Summary

When designing interlocking think about what you are doing. You might think that all the different junction signals on a gantry need to be interlocked to orevent more than one being pulled off at a time - but that is not necessary, because only one will ever match the correct point positions at a time.

import