Charing Cross (Northern Line) tube crash
Encyclopedia
The Charing Cross tube crash occurred at 08:32 hours on 10 March 1938, when two Northern Line
trains collided
near Charing Cross
(now Embankment
). Twelve people were slightly injured. The cause was a wrong-side failure
of the automatic signals
; an electrician had rewired a faulty signal, S94B, so that it showed green too soon after a preceding train had passed. Although the British Rail accident at Clapham Junction
in 1988 bore resemblances to this very rare type of accident, there were significant differences. In fact the ramifications of this accident were to cause a major rethink of British Railway Signalling.
It was during the morning rush hour when the departure signal at Waterloo station was operating intermittently, in that sometimes it turned green but sometimes it didn't, forcing the driver to proceed under the 'stop and proceed' rule applicable to underground working after a five minute wait. The signal engineer for the area was unavailable and so an engineer was summoned from Kennington station
. When he arrived, he gave instructions for the platform staff to hold the next train even if the signal turned green, while he entered the tunnel and looked for the fault.
He quickly found a signalling relay that although it was de-energised (known as 'down' in railway signalling speak), there was nevertheless a voltage across a normally closed contact (known as a 'back contact' in railway signalling speak), indicating that the contact was faulty. As a temporary measure to get the trains moving, he shorted out the contact with a piece of wire terminated in two crocodile clips. The engineer was mindful of the fact that he had substantially shortened the overlap distance of the signal. When he arrived back at the station he instructed the platform staff to hold every train for one minute after the signal turned green. He then went in search of a second wire with the intention of temporarily connecting the faulty contact to an unused contact on the same relay restoring normal operation. It was while he was searching that the collision took place just outside Charing Cross station.
In the enquiry, the signal engineer was held wholly to blame, because although his temporary fix was reasonable under the circumstances, the instructions that he gave to the platform staff were incorrect. The holding of the train for one minute after the green aspect was reasonable, but the driver should have been instructed to, "... proceed at caution and be prepared to stop short of any obstruction". The absence of the last instruction meant that the driver would proceed at full speed and be unable to stop short of another train.
The inquiry and final report had an unexpected twist, because the engineer offered in his defence that he had introduced the equivalent of a single point failure, exactly what would have happened had the contact stuck closed. He pointed out that it was a legal requirement that signalling systems should be immune from single point failure modes, and the board of enquiry had no alternative but to agree.
As a result, the berth circuit (not to be confused with the 'berth track circuit') was developed whose purpose was to detect contacts that were closed when they shouldn't have been and to rupture the relay supply fuse if such a condition was detected forcing the controlled signals to show an unchanging danger indication. The berth circuit was retrofitted to every automatic signalling system in Britain.
Northern Line
The Northern line is a London Underground line. It is coloured black on the Tube map.For most of its length it is a deep-level tube line. The line carries 206,734,000 passengers per year. This is the highest number of any line on the London Underground system, but the Northern line is unique in...
trains collided
Rear-end collision
A rear-end collision is a traffic accident wherein a vehicle crashes into the vehicle in front of it, usually caused by tailgating or panic stops...
near Charing Cross
Embankment tube station
Embankment is a London Underground station in the City of Westminster, known by various names during its history. It is served by the Circle, District, Northern and Bakerloo lines. On the Northern and Bakerloo lines, the station is between Waterloo and Charing Cross stations; on the Circle and...
(now Embankment
Embankment tube station
Embankment is a London Underground station in the City of Westminster, known by various names during its history. It is served by the Circle, District, Northern and Bakerloo lines. On the Northern and Bakerloo lines, the station is between Waterloo and Charing Cross stations; on the Circle and...
). Twelve people were slightly injured. The cause was a wrong-side failure
Wrong-side failure
A wrong side failure describes a failure condition in a piece of railway signalling equipment that results in an unsafe state.A typical example would be a signal showing a 'proceed' aspect when it should be showing a 'stop' or 'danger' aspect, resulting in a "false clear"...
of the automatic signals
Railway signal
A signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers. The driver interprets the signal's indication and acts accordingly...
; an electrician had rewired a faulty signal, S94B, so that it showed green too soon after a preceding train had passed. Although the British Rail accident at Clapham Junction
Clapham Junction rail crash
The Clapham Junction rail crash was a serious railway accident involving two collisions between three commuter trains at 08:10 on the morning of Monday, 12 December 1988....
in 1988 bore resemblances to this very rare type of accident, there were significant differences. In fact the ramifications of this accident were to cause a major rethink of British Railway Signalling.
It was during the morning rush hour when the departure signal at Waterloo station was operating intermittently, in that sometimes it turned green but sometimes it didn't, forcing the driver to proceed under the 'stop and proceed' rule applicable to underground working after a five minute wait. The signal engineer for the area was unavailable and so an engineer was summoned from Kennington station
Kennington tube station
Kennington tube station is a London Underground station in Newington/ Walworth on Kennington Park Road, on both the Charing Cross and Bank branches of the Northern Line. Its neighbours to the north are Waterloo on the Charing Cross branch and Elephant & Castle on the Bank branch; the next station...
. When he arrived, he gave instructions for the platform staff to hold the next train even if the signal turned green, while he entered the tunnel and looked for the fault.
He quickly found a signalling relay that although it was de-energised (known as 'down' in railway signalling speak), there was nevertheless a voltage across a normally closed contact (known as a 'back contact' in railway signalling speak), indicating that the contact was faulty. As a temporary measure to get the trains moving, he shorted out the contact with a piece of wire terminated in two crocodile clips. The engineer was mindful of the fact that he had substantially shortened the overlap distance of the signal. When he arrived back at the station he instructed the platform staff to hold every train for one minute after the signal turned green. He then went in search of a second wire with the intention of temporarily connecting the faulty contact to an unused contact on the same relay restoring normal operation. It was while he was searching that the collision took place just outside Charing Cross station.
In the enquiry, the signal engineer was held wholly to blame, because although his temporary fix was reasonable under the circumstances, the instructions that he gave to the platform staff were incorrect. The holding of the train for one minute after the green aspect was reasonable, but the driver should have been instructed to, "... proceed at caution and be prepared to stop short of any obstruction". The absence of the last instruction meant that the driver would proceed at full speed and be unable to stop short of another train.
The inquiry and final report had an unexpected twist, because the engineer offered in his defence that he had introduced the equivalent of a single point failure, exactly what would have happened had the contact stuck closed. He pointed out that it was a legal requirement that signalling systems should be immune from single point failure modes, and the board of enquiry had no alternative but to agree.
As a result, the berth circuit (not to be confused with the 'berth track circuit') was developed whose purpose was to detect contacts that were closed when they shouldn't have been and to rupture the relay supply fuse if such a condition was detected forcing the controlled signals to show an unchanging danger indication. The berth circuit was retrofitted to every automatic signalling system in Britain.