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A deadly combination of a London ‘pea-souper’ fog and an inexperienced signalman resulted in the worst ever accident on Britain’s Southern Railway 70 years ago today.

The fog which shrouded London on the autumnal morning of October 24th, 1947, was even thicker than usual, limiting vision to just 20 yards in many places. That caused problems for most people, but for those whose job required a good line of sight it was not only problematic, but dangerous.

That was why railway signalmen has backup systems to warn them of danger even if they couldn’t see it, but much of the equipment was temperamental and unreliable, so that some signalmen did not trust it. The crash at South Croydon Station involved just such a lack of trust, although on this occasion the equipment was working as it should.

The disaster involved two electric commuter trains, both overcrowded with rush-hour travellers. One, travelling from Haywards Heath to London Bridge, carried 800 people but was held up for five minutes at South Croydon. Some distance behind it and travelling on the same line to London Bridge was the commuter train from Tattenham Corner, this one carrying about 1,000 passengers.

The signal system meant both trains should not be on the same section of track at the same time. In other words, the Tattenham Corner train should not enter that section until the Haywards Heath train had moved on and the ‘all-clear’ signal was given. But on this morning, the inexperienced porter-signalman at Purley Oaks, who had only recently returned from wartime service in the army, could not see the first train held up at the station and simply forgot it was there.

His backup safety system, known as the “Sykes Lock and Block” apparatus, did its job by warning him that the line ahead was not clear. But the equipment had been temperamental in the past and the signalman, believing it was faulty again, used his release key to override it. The result was catastrophic, as the Tattenham Corner train, still travelling at 40mph, ploughed into the back of the stationary Haywards Heath train.

No-one could imagine the horror for the driver of the second train, as the rear of the first one suddenly appeared out of the thick fog, but it lasted only seconds as the driver was instantly killed. Another 31 passengers also perished in the carnage, with 183 others injured and 58 requiring treatment in hospital. Most of the dead and injured were on board the second train, which sustained the worst damage.

Parts of the railway network had suffered neglect during the Second World War, which had only ended two years previously, as the national war effort demanded priority. The South Croydon rail disaster highlighted an urgent need to look anew at the increasingly crowded railways, and especially their ageing and untrustworthy safety systems.

Traditional ‘semaphore’ railway signals were gradually replaced with a new and more effective system of coloured lights, more easily visible even in fog, while new automated safety measures were also introduced. They did not end railway crashes, but never again was the loss of life so severe on that part of the network.

• To see an archive British Pathé newsreel of the South Croydon rail disaster, click here.

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