The last bottleneck connecting Dundalk with Cork will be removed following the securing of funding for road projects in Dublin and Wicklow.
Work will start next year on upgrading the Newlands Cross junction outside Dublin on the N7, which will mean continuous motorway from Dundalk to Cork.
The N11 will also be upgraded to four lanes between Arklow and Rathnew.
The Minister for Transport Leo Varadkar said funding of €100m is set to be provided under a public private partnership with contributions from the European Investment Bank and Bank of Ireland.
He said this is the first such road projects in a number of years and both are due to be completed by 2014.
"It's particularly welcome to be able to remove the last traffic light between Dundalk and Cork, on one of Ireland's most important and busiest routes," he said.
