The final stretch of dual carriageway linking Dublin and Belfast was opened today, shortening the journey time between the two cities to around two hours.
When the M1 motorway was constructed in Northern Ireland in the 1960s it ran westwards from Belfast.
The A1 road to Newry and the border branched off outside Lisburn.
Now the dual carriageway and motorway on both sides of the border from Dublin to Belfast is complete.
The road is opening five months ahead of schedule and will shorten journey times by around ten minutes.
It will link in with the M1 motorway from Dublin to Dundalk, which was completed a few years ago.
Northern Ireland Deputy First Minister Martin McGuinness and Regional Development Minister Conor Murphy opened the 12km bypass at 11am.
Taoiseach Brian Cowen also attended the opening and hailed the road as a boost for the whole island.
'It brings all of us closer,' said Mr Cowen, who said the development would also bring economic and social benefits.
