Government engineers have said the proposed A5 dual carriageway link between Londondery and Dublin is better value, will be safer and will affect fewer land-owners than alternative proposals, according to the roads minister.
Regional Development Minister Danny Kennedy told the Assembly he would reserve judgment on the major Western Transport Corridor until completion of an ongoing public inquiry.
The dual carriageway will run from Derry to Aughnacloy, with the route helping to link Donegal to Dublin.
The minister said his department's engineers had considered the merits of providing a new dual carriageway against upgrading the existing route, or adding a “two plus one” carriageway, which effectively involves creating over-taking lanes.
He said they found that a new dual carriageway was the most cost-effective project, with the alternatives expected to take up a greater amount of land and likely to affect 50 properties, as opposed to the planned demolition of seven homes for the dual carriageway route.
The Assembly debate came after Sinn Fein tabled a motion backing the A5 scheme.
Members of the DUP and UUP raised concerns over the A5 plan and called for alternatives.
Ulster Unionist objector Ross Hussey agreed the route needed to be upgraded, but he cited concerns over the environmental and social impact of upgrading to a dual carriageway, plus concerns over pollution and the cost of the project.
The DUP's Lord Morrow challenged Jim Allister, who claimed the project had the effective backing of the DUP.
The TUV leader said: “This is not a road project, it is a political project.”
The A5 Western Transport Corridor is the largest proposed single roads project in Ireland and is estimated to cost between £650m and £850m. The Executive and the Republic agreed in July 2007 to bring forward projects to provide dual carriageway standard on the A5 (Aughnacloy to Derry) and the A8 (Belfast to Larne) with the Irish government contributing £400m.