AHB Level crossing timings

There was supposedly a problem with one of the AHB crossings on the Felixstowe branch this morning. A MOP rung the signaller stating a train had gone over the crossing with the barriers still in the air. Q the blokes in orange from Network Rail and after a lengthy investigation, train cancellations and delays and after speaking to the MOP again, it was revealed the MOP was mistaken and hadn't actually witnessed anything.

Im not saying this is the same here but make sure you are certain you are correct before reporting it!!

Im not saying this is the same here but make sure you are certain you are correct before reporting it!!

Im not saying this is the same here but make sure you are certain you are correct before reporting it!!

When in the sequence does the AHB indicator in the box go from 'raised' to 'working'? Is it as soon as the amber road light first illuminates, the red road lights start flashing or the barriers start lowering?

On a double line, as Clive explains, the train first strikes in (a minimum of?) 10 seconds before the sequence starts (to prevent the barriers raising behind a train on the opposite line). Is there then a second treadle to start the actual crossing sequence, or does it just count to ten?

The working party report of 1979 relaxed many of the stringent measures imposed after Hixon and formed the basis for current level crossing protection. Major changes included a reduction in strike-in times and changes to timing sequences, removal of the neon ‘ATC’ signs, single means of strike-in initiation, facility to use AOCL (formerly OCFL) on double lines, and introduction of AOCR. Signing arrangements were also altered. Strike- in treadles were no longer required, except where there was evidence of track circuit shunting problems. Bi-directional controls were introduced for double line crossings with a consequent need for time releases for the track circuit stick control circuits. A complete new set of typical circuits was issued to accompany these changes.

When in the sequence does the AHB indicator in the box go from 'raised' to 'working'? Is it as soon as the amber road light first illuminates, the red road lights start flashing or the barriers start lowering?

• the amber road lights are supposed to be lit


• the red road lights are supposed to be lit


• the barriers are not proved fully up

On a double line, as Clive explains, the train first strikes in (a minimum of?) 10 seconds before the sequence starts (to prevent the barriers raising behind a train on the opposite line). Is there then a second treadle to start the actual crossing sequence, or does it just count to ten?

And of course History goes full circles because now you have strike in treadles everywhere again!

Note: national policy is now to have two treadles to assist each track circuit operation, but this could be achieved by other means e.g. axle counters.