High Quality Content by WIKIPEDIA articles! The M1 is a motorway in Northern Ireland. It is the longest motorway in Northern Ireland and runs for 38 miles (61 km) from Belfast to Dungannon through County Down and County Armagh. It forms part of the route via the A1 in Northern Ireland (N1/M1 in the Republic of Ireland) between Belfast and Dublin as well as being a part of the unsigned European E01 and E18 routes.