A "catalogue of failures to act over a number of years" caused the Paddington train crash in 1999, a court has heard.
The crash killed 31 people and injured hundreds
There were failings across all levels of staff at Railtrack, which maintained the railways - the sentencing hearing at Blackfriars Crown Court was told.
Philip Mott QC, for the Crown, compared the crash, which killed 31 and injured more than 400, to a terrorist atrocity.
Network Rail, which replaced Railtrack, earlier admitted safety breaches and is now facing an unlimited fine.
The crash happened on 5 October, 1999, when a Thames Train went through a red light at Ladbroke Grove, shortly after leaving Paddington in west London.
It hit a Great Western express, causing the first-class carriage at the front to burst into flames.
Mr Mott said a catalogue of failures to act over a number of years had meant drivers - both inexperienced and experienced - passed through one signal at red on seven separate occasions.
"It was the last protection against a head-on collision with a train travelling at high speed," he said.
"The sad conclusion... is that the failings started with the culture at the top of the body responsible for the track and affected staff at all levels of the organisation."
Mr Mott said: "This was no terrorist attack, but to many who have suffered and still suffer it must have seemed as senseless and unnecessary."
He added that the devastating impact was compounded by "fireballs of diesel vapour" which shot through wrecked carriages".
The number of dead and injured was so high, there was a danger they may appear to be "mere statistics", he said.
"But no one who has studied the evidence in this case can fail to be aware of the individual tragedies which lie behind each and every one of those names and numbers."
In October 2006, Network Rail admitted charges under the Health and Safety at Work Act 1974.
Train operator Thames Trains was fined £2m for the crash in April 2004.