A wagon being propelled by a rail-mounted crane near Port Glasgow station in Inverclyde struck the workers at around 8.55pm on March 15 during engineering works.
One of them became stuck between the wagon and a track panel which had previously been set down on the railway by a second crane.
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The worker was later freed by the emergency services and was treated in hospital for injuries.
The Rail Accident Investigation Branch (RAIB) said on Thursday it has begun an investigation into the incident to determine the sequence of events that led to it.
Investigators will consider the actions of staff involved and anything which may have influenced their decisions, how the cranes were controlled, planning and coordination arrangements for the work, and how staff were managed and trained.
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The investigation is independent of the industry regulator, the Office of Rail and Road (ORR).
The RAIB said: “We will publish our findings, including any recommendations to improve safety, at the conclusion of our investigation.
“This report will be available on our website.”
A spokesperson for the ORR said: “We are investigating the incident at Port Glasgow, working with the British Transport Police and the RAIB to establish what led to the events.”
British Transport Police said it was unable to comment on the investigation.
