Up to 700 sets of points across the entire rail network are being checked following the Cumbria train crash.
One woman died in the crash near Kendal on Friday evening. Eight people were seriously hurt and remain in hospital.
The investigation is focusing on a set of points which the Virgin Trains Pendolino ran across before derailing.
One rail expert said he had been told the points could have had loose bolts, and drew comparisons with the 2002 Potters Bar crash, which killed seven.
Network Rail, which is responsible for maintaining track, said engineers hoped to complete checks of between 600 and 700 sets of points by the end of the day.
How crash unfolded
The checks are being made on sections of older tracks on which trains travel above 85mph.
Points are where the line divides and the train is sent either to the left or to the right onto a different track.
Rail expert Christian Wolmar told BBC News 24 he understood the circumstances of the crash were similar to those in the Potters Bar crash.
In that crash, in May 2002, seven people died and 76 were injured when poorly maintained points derailed a train.
"From what I understand, they have found these points in a similar condition to those at Potters Bar, with some missing nuts and the stretcher bar, which keeps the rails properly apart, apparently loosened," he said.
"We are devastated by the death of our Nan "
Mr Wolmar said it was up to Network Rail to ensure that the points were properly maintained and that "things like loose bolts and nuts were tightened up regularly".
He added: "But there is also the possibility that these nuts and bolts were maintained in the wrong way, or not sufficiently maintained, and that's why they were in that condition."
The chief executive of Network Rail, John Armitt, acknowledged that there might have been a points failure. He said the points were last serviced earlier this month.
CONTACT NUMBERS
Police said it was "little short of a miracle" that more people did not die in the accident.
Jonathan Duckworth, chairman of the Paddington Survivors Group, told BBC Radio Five Live he was also surprised so few people were seriously hurt.
"I think that's a testimony really to the rolling stock and how design changes have made the rolling stock very much safer than it was say 20, 30, 40, 50 years ago," he said.
Relatives of the woman who died - 84-year-old Margaret Masson, of Glasgow - have spoken of their loss.
Mrs Masson's daughter and son-in-law, Margaret and Richard Langley, were hurt in the crash and are still in hospital.
Her granddaughter Margaret Jones, 41, said the family was "distraught" by events.
"We are devastated by the death of our Nan and about Mum and Dad being so very poorly," she said.
A total of 22 people were taken to three different hospitals after the accident. Dozens more people received minor injuries.
Of the eight patients who were seriously injured, five are improving while three remain in a serious condition.
The driver of the train, Iain Black, suffered a broken collar bone and a broken bone in his neck, his union Aslef has said.
He is expected to remain in hospital for about a month.
Both the union and Virgin boss Sir Richard Branson said the former police officer, 46, was "a hero".
Mr Black had come around a corner, Sir Richard said, to find the line defective before the train started to leave the tracks.
"He's carried on sitting in his carriage for nearly half a mile, running the train on the stone - he could have tried to get back and protect himself but he didn't, and he's ended up quite badly injured."
Virgin Trains said the line may not reopen to passengers services until during the week beginning 5 March.
In the meantime, train services from the south are terminating at Lancaster and Preston, while train services from the north are terminating at Carlisle, and there is a replacement bus service between the two.
Passengers who intend to travel on the West Coast Main Line can check the latest information with National Rail Enquiries.
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