The track workers, operating on a bridge on the West Coast main line in Lancashire, were reliant on getting visual and audible warnings of approaching trains as their view was restricted by the curvature of the track.
But they received no warning that an Edinburgh to Manchester Airport train was approaching.
The Rail Accident Investigation Branch (RAIB) said: “They were forced to take immediate evasive action when the train first became visible, approximately four seconds before it reached the site of work.
“Some staff were unable to reach a safe position and pressed themselves against the bridge parapet.”
The RAIB has launched an investigation into the incident that happened south of Hest Bank, between Carnforth and Lancaster, on the afternoon of
22 September this year.
The RAIB said the track workers comprised contract staff and a controller of site safety employed by Network Rail. They were packing ballast under sleepers on the main line on a small bridge.
A lookout-operated warning system (Lows) was being used to give warning of approaching trains because of the gang’s restricted view.
The system is designed to allow lookouts to signal the approach of a train by operating two toggle switches on a Lows lookout unit. This transmits a radio signal to a Lows static unit which then gives both visual and audible warnings.
The RAIB said that on the afternoon of the near-miss, the Lows equipment was being operated by two NR lookouts, one on each side of the “site of work” and each equipped with an Lows lookout unit.
The lookout watching for trains on the line was located about half a mile from the site of work, in a position which gave him a good view of trains approaching from the north.
The static unit was located near the track workers. The Lows equipment is reported to have been both tested and operating normally prior to the incident.
The RAIB said: “Our investigation will examine the reasons why no warning was provided to the track workers.
“It will also consider the sequence of events and factors that may have led to the incident, and identify any safety lessons.”