Case study: automatic warning system fixed

08 September 2022

Possibility of a SPAD or train accident highlighted in report.

Railway automatic warning system

The AWS (automatic warning system) is faulty on signal HT6 on the Southern route. Network Rail knows but it has not been fixed for over two months. It would usually be fixed more quickly.
The fault means drivers will always receive a horn notification in the cab even if signal HT6 showed a green aspect. This normally should not happen.
The signal has therefore been restricted to always display single yellow aspect so it matches the driver notification (both the horn and single yellow indicate a warning and prompt drivers to slow down). The next signal, HT4, has been put under approach control so it clears to green when the train approaches, indicating it is safe to proceed.
This workaround is appropriate but would usually only be in place for a few days. Drivers could become complacent and it could result in a signal passed at danger (SPAD) or train accident.

The fault has now been fixed. It is working correctly and there have been no issues raised since.
AWS should be fixed as soon as possible. Complications with the work on this signal caused delays (access, bolts needing to be cut off from the middle plate, resourcing). We will work to reduce these issues in future.