Two track workers were killed by a train while there was no official lookout in place, a report has found.
Michael Lewis, 58, and Gareth Delbridge, 64, died while carrying out engineering work for Network Rail on the line near Port Talbot, South Wales, on July 3.
An interim report by Network Rail said that while one person was meant to act as an unofficial “distant lookout” and give warning of oncoming trains, they became involved with track work and were unable to alert their colleagues.
A team of six employees had split up into two groups of three on the day, which “compromised” the number of lookouts available, the rail firm said.
It said it meant “there was no safe system of work in place” for workers who were freeing, lubricating and retightening crossing bolts on the line.
One group, including Mr Lewis and Mr Delbridge, were wearing ear defenders while working on a part of the track at 9.51am, and were unaware of the Swansea to London Paddington service approaching at 70mph.
The report said the train driver used high and low tone of the horn, before using two long continuous blasts of low tone, in an attempt to warn the group.
But it said it was “uncertain” whether using a series of short high tones warnings instead could have resulted in the workers becoming aware of the train earlier.
Mr Lewis and Mr Delbridge were subsequently hit and killed, while the third worker, who witnessed the incident, suffered “severe shock”.
The report also noted other employees believed that they had been working in the most “effective way”, with no evidence of previous near misses, which had “potentially led to overconfidence and a culture that delivered work ‘their way’.”
Martin Frobisher, Network Rail’s safety director, said the firm would continue to investigate the cause of the accident before it made recommendations for the future.
He said: “The whole railway family shares the loss of Gareth and Spike.
“Nothing will lessen the pain but understanding what went wrong and learning from that will, I hope, go some way to reassure all those affected that we will do all we can to stop it ever happening again.
“Today is the first step in that journey as we share an initial investigation into what happened.
“We will continue for several months to look deeper into the root causes before we make recommendations for our organisation and all of our people for the future.”