Motorists are being warned the A404 motorway in Berkshire will be closed to traffic as work on a £10m project to replace a bridge begins.
Work on demolishing the Western Region Railway Bridge near Maidenhead began in August last year.
Six 20-tonne steel beams, forming part of the bridge deck of the new structure, will be lifted into place.
The Highways Agency said the work will end at 1800 BST on Sunday and diversion routes were in place.
A spokesman for the agency said: "The new structure will be far easier to maintain and is designed to last well into the 22nd Century."