The first giant beams creating a new A14 bridge across the east coast main railway line near Offord have been lowered into place.
Trains on the line were halted for four hours early on Sunday morning when two pairs of steel girders, weighing 100 tonnes each, were lifted by a 500 tonne crawler crane.
Work was completed with an hour to spare during the operation which involved the railway's overhead power lines being isolated.
A further three beams will be craned into position in the coming weeks to form the bridge which is part of the £1.5 billion upgrade of the A14. The bridge will carry three lanes of traffic in each direction when the road is complete by the end of 2020.
David Bray, Highways England project director, said: "The successful installation of the first two bridge beams over the East Coast main line railway is the culmination of two years of planning and the fact that the team was able to do this in around three hours is a credit to the level of expertise at our disposal on this project.
"We have just marked our first year of construction and we are a quarter of the way in to our programme already."
He said: "The improvements we are delivering between Cambridge and Huntingdon are vital for the local area and for the country's economy.
"We set out to deliver world-leading infrastructure improvements a year ago, this is exactly what we have been doing so far and we look forward to continuing to deliver our challenging programme in record time."
A crossing over the River Great Ouse is being built next to the rail bridge as part of a long-awaited scheme to upgrade 21 miles of the congested road which includes a major bypass for Huntingdon.
The road is expected to be ready by the end of 2020, although some work will continue in the Huntingdon area, including the demolition of the A14 viaduct above the town's railway station.