Minister for the Environment Dick Roche is to allow the controversial M3 motorway to proceed through the Tara-Skryne valley in Co Meath.
Mr Roche told The Irish Times there was "no way" he could revisit a decision made by An Bord Pleanála in August 2003 to approve the present proposal.
"I am where I am," he said. "This has gone through the planning process."
He intends to issue licences for archaeological excavations along the route.
Mr Roche's decision follows receipt of an 18-page letter from National Museum director Dr Pat Wallace, who makes it clear that he is against the chosen route and, in particular, a proposed interchange to the north of the Hill of Tara.
Dr Wallace's view that the motorway would have a "demeaning" impact on the Tara landscape was echoed in a statement issued yesterday by more than 80 academics and scholars worldwide appealing to the Government to change the route.