The N40 is the Cork Southern Ring Road. Formed from a section of the N25 route that connects Cork with the port of Rosslare, the N40 was legally created in February 2012. From April to August of the same year, signage along the route was updated.
The route, as N25, had been opened in stages from 1990 to 1999, with some grade separations opening in 2006 and 2013. The Kinsale Road (N27) to Douglas segment was a primer, opening to traffic in 1990. Next was Douglas to Rochestown (N28) in 1992. This incorporated a piece of what would become the N28. Then a longer section (3.6 km) from Bishopstown to Kinsale Road (N27) opened in 1995. These were all dwarfed by the Jack Lynch Tunnel, a 4 km segment that linked the east end (Rochestown/N28) to the N8 at Dunkettle via a tunnel under the River Lee. This opened to traffic in 1999 and featured fully grade-separated junctions, unlike most of the rest of the road.
Finally, the western end of the road was extended 8.6 km (3.3 km of which would become N40) further west with the opening in 2004 of the N22 Ballincollig Bypass. This new road also created a narrow-profile dual carriageway to connect with the east end of Ballincollig.
With the mainline now completed, attention focussed on removing at-grade intersections. A flyover was built at Kinsale Road (N27) in 2006, and in 2011 work started on the large Bandon/Sarsfield Road grade separations. This project, which opened in 2013, is an extensive rehabilitation of the stretch, adding frontage roads and flyovers, making it motorway-standard.
There is one final at-grade junction left - at Dunkettle, a roundabout is due to be thoroughly overhauled in the coming years as a complex interchange exchanging traffic between the N8 (into Cork City), the M8 (motorway to Dublin), the N40 Southern Link Road, the N25 east towards Midleton and a nearby associated junction at the industrial complex of Little Island. The scheme has its own website.
It is clear that the whole road will eventually be a free-flowing motorway-grade dual carriageway. The question of whether it will ever be redesignated a motorway arises. As of now, however, there is no sign that this will happen. The signage replacement that occurred in 2012 would have been wasted money.
Update 06/10/2020:
The full Dunkettle Interchange was retendered and is due to start by the end of the year. It will take several years to build.
Update 20/01/2021:
Dunkettle Interchange construction got fully underway in December. It is expected to open in stages until autumn 2023.
Update 24/10/2021:
In the same way that the Galway Bypass was rebranded as something like Galway Tranportation Project, so it would hopefully include public transport and cycling facilities aswell as a new road, the Cork Northern Ring Road has been relaunched as "Cork Northern Transport Project".
It seems it will be a new road and a Park and Ride at a new Monard railway station.
A website has been launched, which is a little light on content for now.
Wikipedia page
Pictures of this road (none yet)