Railway block code


The railway block signalling bell code is a system of bell rings used in Great Britain to communicate between manually operated Signal Boxes. Each signal box would have a bell circuit to the box on either side of it along the line. The equipment would consist of a plunger or tapper which if pressed, rings the bell in the neighbouring box. The neighbouring box would have a key for communicating back, therefore each box has a key which rings the bell in the other box. Where a signal box communicates with more than one other box, each bell would have a different tone, so that the signalman could tell them apart by ear.

Examples

Although codes varied from region to region, the following shows a few selected standard UK bell codes:
CodeMeaning
1 bellCall attention
2 bellsTrain entering section
2 - 3 bells Is line clear for light engine?
2 - 2 - 1Is line clear for empty coaching stock train?
3Is line clear for stopping freight train?
3 - 1Is line clear for stopping passenger train?
3 - 1 - 1Is line clear for express freight train?
4Is line clear for express passenger train?
4 - 1Is line clear for mineral or empty wagon train?
2 - 1Train arrived
3 - 3Blocking back outside home signal
5 - 2Release token
2 - 5Token replaced
5 - 5 - 5Opening signal box
7 - 5 - 5Closing signal box
6Obstruction danger
4 - 5 - 5Train running away on Right Line
2 - 5 - 5Train running away on Wrong Line
16Testing bells and instruments

Typical use

These would be used as follows between two signal boxes A and B. Assume a train is to pass from the block controlled by A to the block controlled by B. This must be agreed and permitted by the signalman in box B. Here is the sequence of bell codes and associated actions:
  1. Box A sends 1 bell to box B.
  2. Box B replies with 1 bell to box A.
  3. Box A sends 4 bells to box B.
  4. Box B sends 4 bells to box A.
  5. Box A sends 2 bells to box B. This is sent as the train passes box A and enters the block controlled by B.
  6. Box B sends 2 - 1 bells to box A.