Network Rail and rail services company Amey were fined a total of £500,000 today following the partial derailment of a high-speed train.
The companies had pleaded guilty to breaking health and safety laws in November 2002.
The Old Bailey was told that 450 passengers were on board the Swansea to Paddington service as the wheels of one of the eight coaches came off the track.
The 8.05am train was travelling at 120mph through Southall station in west London.
The train went on for a further two miles before coming to a halt.
"It must have been exceptionally frightening for the 450 fare-paying passengers, not to mention the frustrating inconvenience of a two-and-a-half- hour evacuation," said Judge Richard Hone.
An official report into the accident had concluded that it was "an unlucky and unpredictable event".
Network Rail was fined £200,000 and Amey £300,000. They were ordered to pay costs.Reuse content