M20 Rosbrien Interchange (Limerick) to Patrickswell
The route starts at junction 1 at the Rosbrien interchange where it connects to the M7 and the N18 which together form the Limerick Southern Ring Road. The route continues from this interchange as motorway. This route was redesignated as motorway in August 2009. The route bypasses Dooradoyle and Raheen, through which the old N20 route used to run until the early 2000s. Interchanges and link roads connect to these locations. Two further interchanges are located on the motorway, at either end of Patrickswell. At the latter, the N20 route leaves the main road, i.e. one must diverge from the motorway to stay on the N20.
A wide two lane road brings traffic along the Croom bypass. Past this new section of road, narrow two-lane road commences, ending at Charleville. The route passes through the town, running along Main Street. The road between Charleville and the next town, Buttevant is of similar design. At Mallow a relatively high specification road is encountered, with an older bypass of the town passing up the hill from it as dual carriageway. A viaduct brings the road across the Blackwater River and Valley. The rest of the route to Cork is of high quality wide two lane, with a section of 2+1 road south of Mallow. The route becomes dual carriageway on the approach to Cork. New relief roads in Cork bring the route into the city centre while avoiding the winding streets through which the route ran until around 2000.
Under the government's cancelled Transport 21 initiative, the Atlantic Corridor road project aimed to link Letterkenny to Waterford via Limerick and Cork with high quality roadway. A major part of this project involved the upgrading of the N20 route between Cork and Limerick. It was proposed to upgrade or replace the entire N20 with a new M20 motorway, approximately in length, with up to eight newly constructed junctions or re-configured junctions. It was to be constructed in two stages: a southern section and a northern section. It is hoped that this project will be progressed as a PPP scheme. Details of progress on the scheme can be found on the Cork National Roads Office website. The first segment of M20 motorway came into existence on 28 August 2009 following the approval by the Minister for Transport to redesignate a of existing N20 dual-carriageway between Rossbrien and Attyflin as motorway. On 10 November 2011, owing to funding issues caused by the Irish financial crisis, the government announced that the planned completion of the M20 motorway is to be shelved for the foreseeable future, along with a number of other infrastructural projects. In 2013, the National Roads Authority carried out an extensive upgrade of all directional road signage along the N20 national route, fuelling speculation that it will be some time before plans for a new motorway from Limerick to Cork are revisited. In October 2017, it was announced by the TaoiseachLeo Varadkar that the new motorway is due to be built by 2023, projected to cost over €800 million. It has been described as one of the biggest infrastructure projects of its kind for many years in Ireland.
