A points failure has been identified as the likely cause of yesterday’s train derailment at Potters Bar in Hertfordshire, England, which claimed the lives of seven people and injured dozens more.
The railway company, Railtrack, revealed there was evidence of a fracture in a front stretcher bar - one of the supports on a point system, just south of the station - that caused nuts holding them in place to shear off.
Railtrack chief executive John Armitt said as the four-carriage 12.45pm King's Cross to King's Lynn service passed over them, the points moved, causing the train to come off the tracks.
He told a news conference at Hertfordshire Police headquarters in Welwyn Garden City that the focus of the investigation would now be to find out why the nuts came loose.
But he said more than 400 checks had been carried out on similar points systems around the rail network in the last 36 hours and no defects of a similar nature had been found.
"The nuts that held the two other supports in place became detached which resulted in the front section bearing all the pressure," explained Mr Armitt.
"Why the nuts detached is not known."
The points were the subject of a visual check by an inspector only a day before the accident but no defects were reported. The points would not have been touched.
The accident had been "truly unique", Mr Armitt added, but it was not envisaged that any specific speed restrictions would be implemented across the rail network.
Dr Allan Sefton, the Health and Safety Executive's acting chief inspector of railways, also said that initial investigations showed it was a "one-off" incident.
"It's become pretty clear, although we're still at a very early stage, that a single set of points failed as the train passed over it," he said.
"That led to the derailment of the fourth carriage of the train.
"While we are pretty clear that that was an initial cause of the derailment and accident, we are a long way from being able to gather conclusive evidence about the actual root cause that led to the failure."
The points are now to be subject to forensic and metallurgic tests before a firm conclusion could be reached, he added.
Friday's accident was the latest in a series of tragedies to have hit Britain's railways since they were privatised by the Conservative government of former Prime Minister John Major in 1996. Critics say privatisation has affected safety standards.
Seven were killed in a crash in the London suburb of Southall in September 1997. In October 1999, 31 died in a collision at Paddington in west London and 10 died in February last year in an accident at Selby in Yorkshire, northern England.
PA
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