Railway maintenance work which saw two people struck and killed by a train was not due to start until the line was closed, investigators have found.
Gareth Delbridge, 64, from Kenfig Hill and Michael Lewis, 58, from North Cornelly, were working on the signals at Margam East Junction on July 3 when they were hit by a passenger train travelling from Swansea to London Paddington. A third worker was treated for shock but was not injured.
An interim report by the Rail Accident Investigation Branch (RAIB) said planning documents for the work indicate it was due to start at 12.30pm to coincide with the blockage of the line.
But the group of six men working in the area had split up into two groups of three and began their tasks at about 8.50am.
Witness evidence suggests there was a widespread belief at the local maintenance depot that there was "no need to wait" for the planned line closure in the afternoon, the RAIB found.
There was a "general lack of understanding" as to how the planning paperwork should be interpreted, investigators added.
Network Rail said the splitting up of groups also compromised the number of lookouts available. The absence of a lookout "removed a vital safety barrier".
Mr Delbridge and Mr Lewis had also been using a power tool with petrol engine and were wearing ear defenders, which meant they may not have heard the train approaching.
The train sounded its horn several times and three colleagues working on the line had tried shouting to them.
The system of work proposed by the person in control of site safety "was not adopted" and the alternative arrangements "became progressively less safe as the work proceeded that morning", the report added.
The interim report states the RAIB will assess working practices at Port Talbot depot at the time of the accident. They will have "a particular focus on the way that the maintenance teams at Port Talbot depot were managed and supervised" at the time of accident.
Martin Frobisher, Network Rail's safety director, said: "The whole railway family shares the loss of Gareth Delbridge and Michael (Spike) Lewis.
"Nothing will lessen the pain but understanding what went wrong and learning from it is the only way we can make sure it never happens again.
"We will continue to fully support the investigation and the findings and recommendations."
The two victims had worked on the railway for more than 40 years.
The families of the victims have launched a civil claim against Network Rail alleging it was negligent in its duty of care as an employer.