A railway bridge is being knocked down in Oxford and replaced with a new one so the line underneath it can transport more freight from the south.
It is part of a £71m scheme to improve the rail line between Southampton port and Nuneaton, via Reading, Didcot, Oxford and Banbury.
The project should provide a cheaper, quicker and more practical way of transporting goods around the country.
Work will begin in November and is expected to be completed by March 2011.
The road over the bridge will remain closed for the majority of the time.
The upgrade of the bridge that carries the Old Abingdon Road over the railway at South Hinksey is needed to allow 9ft containers to travel underneath it.
Network Rail said much of the traffic on the A34 is caused by HGVs transporting goods to and from Southampton port.
The company said the project would provide extra capacity to get freight off the roads and onto the railway.
Engineers will work over Christmas Day and Boxing Day to remove the existing bridge while the railway is closed.
Network Rail said rail passengers would not be affected and that residents and local businesses would be kept updated throughout the project.
Chris Rayner, Network Rail route director, said: "Britain relies on rail freight to get food onto supermarket shelves, consumer goods into our shops, coal to our power stations and raw materials to manufacturing businesses.
"Rail freight directly contributes £870m to the economy, takes tens of thousands of vehicles off the road to reduce congestion and produces 76% less carbon dioxide than road freight.
"Schemes such as the upgrade of the railway between Southampton and the West Midlands are vital for these benefits to be achieved now and into the future."