The N4 is the major east-west route through Dublin. In the city centre, it follows opposite sides of the River Liffey. Between the M50 ring road and the centre, it is dual carriageway, but with no grade separations. It experiences heavy traffic.

The oldest section to be dualled was undertaken in 1984 between the east end of Lucan and Palmerstown, opening that summer. The Lucan bypass opened in November 1988, and the Chapelizod bypass on the 1st June 1989. The opening of an initial segment of the M50 in 1990 created a large roundabout junction between Palmerstown and Lucan. In 2008, the M50/N4 junction was grade-separated, and finally, in 2009, the part west of the M50 as far as west Lucan was 6-laned and access-controlled.

The N4 east of the M50 is a different story. The last upgrade it saw was in 1989. With such a high standard to the west, the east is narrow and has only partial access control. Particularly poor is the section through Palmerstown, built at a time when large-scale roads were thought never to be required anywhere in the country. The road has the form of an urban dual carriageway, with three petrol stations and two sets of lights. Pedestrian access is allowed along a section of the southern side.

The junction proposal here would sink the road under the Kennelsfort road with an overpass. A frontage road would link the junction to The Oval to the east, with the median closed there.

The scheme's major issue is that the site is right next to the old town centre of Palmerstown. The town would risk being utterly dominated by the depressed dual carriageway; such arrangements in other countries are often criticised due to the severance they cause. Although the N4 Newcastle Road junction was successfully grade separated (and with 6 lanes) in 2009, that was not adjacent to a town centre. In this day and age, such a proposal would face a lot of community opposition.

Related to this proposal is another to grade separate the Con Colbert Road junction on the N4 further to the east.

Update 2010: The South County Dublin Draft Development Plan 2010-2016 mentions (page 267, item 14) this interchange and says that "either a flyover or a roundabout" is to be provided. This space will be watched.

Update August 2024: There has been no mention of this scheme in a long time, and with the construction in the last 2 years of a large new apartment building on the corner of the site, it would be an inappropriate place to put a flyunder anyway, unless it was roofed over. It is looking like this scheme has been binned.

Wikipedia page on this road