The first motorway in Ireland to be fully completed end to end, the M1 is highly strategically important as it links Dublin with Belfast via the Northern Ireland road network. It was built between 1985 and 2007.
The N1 route begins in O'Connell St in the very centre of Dublin. It uses the street network to make its way northwards via the inner suburb of Drumcondra. When it reaches Whitehall, the old route swings west and continues to the suburb of Swords as R132, while the newer M1 motorway continues directly north and intersects with the M50 Dublin Ring Road. The old road passes under the M50, then enters and passes Swords, all bypassed and dualled in the 1980s.
This was rendered unnecessary by the bypass-of-the-bypass M1 which ran to the east of the old road and bypass and opened in June 2003. Both old and new routes run north parallel northwards, crossing the Broadmeadow estuary and the village of Lusk, before meeting again near "The Five Roads". North of here, the old route has been dualled for a short distance as part of the Balbriggan bypass which opened in 1998. This section was no longer needed once the motorway was completed to the south in 2003. The old route took a winding route through the rapidly growing beachside town of Balbriggan before resuming its northward way outside the town.
The large regional town of Drogheda lies next on the route. When the old road ran through the town, negotiating the narrow bridge over the mighty Boyne river, this town was a major bottleneck. The M1 bypass opened in June 2003 just before the Airport-Balbriggan extension, taking a winding western route through the countryside. In the distant future, it is possible that the Leinster Outer Orbital Road, a toll motorway running in a ring around 40 km from the centre of Dublin, will intersect with the M1 somewhere around this point. The LOOR is still very firmly on the drawing board however and will stay there for some time.
The next spot served by the M1 is the town of Dunleer, which received its bypass early on in 1993, this being only the second segment of the route to open to traffic. The motorway was extended as far as the southern reaches of Dundalk by 2001, but it wasn't until 2005 that Dundalk itself was bypassed with a western peripheral.
The next year saw the motorway extended slightly southwards at the Dublin end with the opening of the Dublin Port Tunnel, though the part of the route that lay within the Dublin urban area was relabelled M50 at this point. Finally, in 2007, the last project on the route was opened to traffic at the far northerly reaches. The old, treacherous winding route towards the border with Northern Ireland was replaced with a modern dual carriageway. Memories of military checkpoints on the old road were buried and the opening of the route was a symbol of the growing rapprochement between Northern Ireland and the Republic.
The Northerners responded in kind in 2010 by connecting the short 4 km part of this route that lay within their jurisdiction to their A1 dual carriageway to Belfast with a project to convert the single-carriageway Newry Bypass to a fully grade-separated dual. With the dualling of this final single carriageway section, the trunk road networks of North and South were connected with high capacity roads for the first time.
On the 8th September 2010, the nation's first service area opened at Lusk north of Dublin between exits 4 and 5, and its second at Castlebellingham between exits 14 and 15 on the 29th September.
Lately, some widening has been taking place. As part of the M50 roadworks which wrapped up in 2010, the section of the M1 between junctions 1 and 2, near the airport, was widened from 4 to 8 lanes. In June 2011, the 2 km section from junction 2 to junction 3 was completed, and the 4-km segment from 3 to 4 was wrapped up two years later in June 2013. A medium-term objective is for this 6-laning to reach Balbriggan at junction 7 by 2035 at the latest, though the whole M1 was built with a wide enough central reservation to enable the works to eventually reach the border.