Network Rail failed to devise a plan to detect the track failure which led to a train derailment despite previous incidents, investigators said.
Cracks in fastenings designed to hold rails in place were not apparent in visual inspections before a freight train came off the tracks in Eastleigh, Hampshire, the Rail Accident Investigation Branch (RAIB) found.
These fractures allowed one of the rails to move under the Freightliner train.
Network Rail had not devised a strategy for routine maintenance inspections to spot the issue despite failures in similar fastenings being identified across several locations in 2015 and 2016, the RAIB said.
The train which derailed at Eastleigh was travelling at 12mph when the incident happened at 11.32am on January 28 last year.
The locomotive ran for around 35 metres before coming to a stop.
Four wagons also derailed, causing “significant damage” to rail infrastructure, the RAIB said.
No-one was injured but passenger services were disrupted for several weeks with trains cancelled and diverted.
The investigation found that Network Rail’s team in Eastleigh “was not effectively managing the maintenance of its track assets”.
An inquiry into a 2016 near-miss between a train and a worker based at the site found that tasks were being carried out later than planned and there was a backlog of work.
Prior to the derailment, the Government-owned company was introducing remedial measures such as reducing the team’s area of responsibility.
But this had not resulted in a notable improvement by the time the accident happened, the RAIB said.
The report made two safety recommendations for Network Rail, regarding how it manages the risk of track fastenings failing, and how it measures the spacing of rails that are not monitored by measurement trains.