The Rail Accident Investigation Branch (RAIB) has opened an investigation after two track workers were struck by a wagon at Port Glasgow on 15 March.
It happened when the wagon was being propelled by a rail-mounted crane within an engineering possession.
One track worker became trapped between the wagon and a track panel, which had previously been placed on the railway by a second crane.
Both cranes were being used as part of the renewal of a section of track within the possession.
The trapped worker had to be freed by the emergency services and was treated in hospital for their injuries.
The rail accident watchdog will investigate the circumstances that led to the accident. It will then publish a report including safety improvement recommendations.
