The M1 motorway in the Republic of Ireland is part of the route from Dublin to Belfast. As of 2004, it runs from south of the M50 ring road in Dublin, to just south of Dundalk town. The motorway was built in several stages as short bypasses connected together, upgrading the N1 route. There is a toll on the motorway south of Drogheda to fund the construction of the motorway. Work is to begin in 2004 on a bypass of Dundalk, extending the motorway to just south of the Border. Outline planning is underway to implement a cross-border stretch of motorway to Newry in County Down. The Northern Ireland authorities have no plans to upgrade the remainder of the route (designated "A1" in the North) from Newry to the M1 (Northern Ireland). Currently, to drive from Dublin to Belfast, one journeys along the M1, N1, A1 and M1 (Northern Ireland).

See also: Roads in Ireland