Work on the largest bridge on the upgraded A14 has been completed, Highways England said.
The River Great Ouse viaduct stretches for half a mile, and it will take traffic over the river and the East Coast Mainline Railway.
It is part of a new 17-mile bypass that is being built to the south of Huntingdon away from the existing A14.
The road is expected to reduce journey times by up to 20 minutes between Cambridge and Huntingdon.
Willie McCormick, of Highways England, said the bridge has taken over 18 months to build, and covers 747 metres.
“Yet when it opens to traffic in 2020, drivers will cross it in less than 30 seconds,” he added.
The old bridge was dismantled by six excavators, with the material recycled and reused in the construction of the new road.
A total of 34 new bridges and structures are being built for the 21-mile improvement to the A14 between Cambridge and Huntingdon for the 85,000 vehicles a day who drive it.
Main construction on the project started in November 2016.