The investigation is being carried out by the HSE and Kent Police after Richard Caddock from Gillingham, Kent, died last Tuesday afternoon. Costain is carrying out road widening work on the motorway at Dartford in Kent.
It is understood that the possibility of Mr Caddock being struck by a car has been ruled out and that investigators are instead focusing on whether the 38-year-old was hit by a lorry on site.
The HSE and Kent Police declined to comment but investigators are believed to be considering whether Mr Caddock heard the lorry above the din of the motorway traffic.
Mr Caddock’s brother Andrew has already spoken to HSE chief inspector of construction Stephen Williams – as well as Costain – about the tragedy.
He said: “The HSE have been very good and so have Costain. I used to work in construction and it’s important to know what’s going on in Richie’s death.”
Costain chief executive Andrew Wyllie, who has made safety the top of his priorities since joining as chief executive in September 2005, visited the site in the aftermath.
In a statement, the firm said: “The thoughts of everyone at Costain are with the family and friends of Richard.
“We are co-operating fully with the investigation and must learn from any lessons arising from it.”
Related links: Costain worker dies on M25