The R639 road is one of Ireland's regional roads. Once designated the N8 national primary road, it was reclassified in stages as the R639 following the progressive opening of sections of the M8 motorway, which rendered the single carriageway N8 redundant as a national primary road. By-passed sections of the old N8 were generally reclassified as R639 as soon as a new section of M8 opened, thereby increasing the length of the R639. With the completion of the M8 on 28 May 2010, the R639 now stretches from Durrow, County Laois to Cork, running through counties Laois, Kilkenny, Tipperary, Limerick and Cork.

The N8 road is a national primary road in Ireland, connecting Cork with Dublin via the M7. The N8 is further classified by the United Nations as the entirety of the European route E 201, part of the trans-Europe International E-road network. The road is motorway standard from junction 19 on the M7 to the Dunkettle interchange in Cork City and is designated as the M8 motorway. From here the route continues into Cork city centre and terminates at the N22 road at St. Patrick's Street. The M8 motorway was completed in May 2010, replacing the single carriageway sections of the old N8 and bypassing towns on the main Cork to Dublin road. It is now possible to travel from Cork to Dublin on the M/N8 in about 2 hours 30 minutes. The route commences just south of Portlaoise, and reaches Cork via the midlands and the Golden Vale of Ireland, through Counties Laois, Kilkenny, Tipperary, Limerick and Cork.