Train derailment in Gloucester was due to badly repaired track
A train derailment in Gloucester happened because a track had been badly repaired, an investigation has found.
A freight train came off the tracks last October four miles from Gloucester station on the line to Newport.
A report by the Rail Accident Investigation Branch (RAIB) found there were dips in the track known as "cyclic top", but repairs had been ineffective.
The Office of Rail Regulation (ORR) is investigating whether health and safety laws have been breached.
The report said a speed restriction should have been put on the stretch of line, on which daily commuter services between Gloucester and Cardiff run.
It showed the train had been travelling at 69 mph (111 km/h) when the rear wagon derailed on 15 October 2013. An empty container fell off a wagon.
The investigation found that Network Rail had identified a problem with the track and carried out repairs, but water flowing beneath the track caused the problem of cyclic top to re-occur.
The RAIB report found: "The severity of the dips required immediate action by Network Rail, including the imposition of a speed restriction for the trains passing over it, but no such restriction had been put in place."
By the time the train stopped at Gloucester station, the rear wagon was severely damaged, the empty container it was carrying had fallen off, and there was damage to four miles of track, signalling cables, four level crossings and two bridges.
The line remained closed for four days while repairs were carried out. Repairs included replacement of 1,300 yds (1.2 km) of track, two sets of points, 300 sleepers, two miles of cable and a level crossing.
The report showed the type of wagon that derailed was susceptible to becoming derailed on track with dips in it, especially when loaded with the type of empty container it was carrying.
The investigation also found there were not enough staff working for Network's Rail's maintenance team.
The ORR said an Improvement Notice was served on Network Rail in June, after it found the Health and Safety at Work Act could have been contravened.
The inspector said an investigation indicated "that you are not conducting your undertaking in such a way as to ensure the safety of train passengers and others so far as it reasonably practicable as you do not have appropriate arrangements to ensure that track maintenance activities which are intended to manage train derailment risks are effectively planned, organised, monitored and reviewed".
Network Rail has been given until next February to make improvements.
Responding to the RAIB report, a Network Rail spokesman said the majority of recommendations outlined in the RAIB report "have either been implemented or are about to be implemented".
"As a result of this incident, we have reviewed the way in which we work and will continue to liaise with the RAIB to make the necessary improvements," they said.
The spokesperson said they would not comment on the ongoing ORR investigation.