Network Rail needs to do a "massive amount" to make level crossings safer, the parent of a teenage girl killed by a train told MPs.
Tina Hughes, who now works with the firm on improving crossings, said that Network Rail had made a number of changes but were only "scratching the surface" of what needed to be done.
Ms Hughes's daughter Charlotte Thompson, 13, and her friend Olivia Bazlinton, 14, were hit by a train in 2005 as they crossed the tracks at Elsenham station footpath crossing in Essex.
Olivia's father Chris Bazlinton, appearing alongside Ms Hughes in front of MPs on the Transport Select Committee, said he believed information about their deaths had been covered up in a "conspiracy of silence".
Key documents highlighting concerns at the crossing were not disclosed until 2010 and the firm was fined £1 million last year for health and safety breaches, with the judge concluding there had been "culpable corporate blindness".
Ms Hughes, who works with Network Rail as its "level crossing user champion", told MPs: "I believe that they have made very significant changes but they are only just scratching the surface of the things that they need to do. There is a massive amount of work that needs to be done."
Mr Bazlinton told the hearing: "I believe Network Rail's actions over the non-disclosure of documents amounts to a conspiracy of silence or worse."
He said he had received "shabby treatment" from Network Rail after the tragedy and added: "I happen to believe that not much has changed at Network Rail in the way that they treat these incidents."
Mr Bazlinton, who broke down at one stage of the emotional session, added: "I still want to know from the people at the top who are ultimately responsible why they withheld those documents and why I should believe it won't happen again.
"This is about accountability now, I think it's important we know what happened within Network Rail. They have never held a proper inquiry, never told us what really happened."
He added: "Somebody is either not telling the truth or did not look through the boxes properly. I don't know how to put it, but any rational person would say there was a cover-up there."
Laurence Hoggart, whose wife Jean, 56, and grandson Michael Dawson, seven, died on the pedestrian crossing in Bestwood Village in Nottinghamshire in November 2008, also gave evidence at the hearing.
In a statement read on his behalf, he said: "This has devastated my life and my family's life. Jean was the backbone of my family and it has broken my heart.
"I think that Network Rail have treated me badly. They wrote just one letter of apology, my solicitors discovered that the crossing was seen to be unsafe by Railtrack in 2000 and their advisers said a bridge should be built.
"That was eight years before they died, nothing was done. They did not care, they were only interested in making money. I think this greed is criminal and I have sued them for compensation and right up until the week before the case was due they stood against me, saying that Jean was 10% or 20% to blame."
Rail safety expert Peter Rayner told the MPs the arrangement at Bestwood was "fundamentally flawed" and resulted in "almost an impossible crossing".
He added that he believed there were "commercial considerations compromising safety and that's the one thing that has to be tackled".
Committee chairwoman Louise Ellman said it appeared from the evidence given by Mr Bazlinton and Mr Hoggart that in both the Elsenham and Bestwood incidents "Network Rail appeared to know that there was a problem but hadn't done anything about it".
She added: "That's a very terrible thing."