The junction of the Naas, Long Mile, and Nangor Roads forms the centrepiece of a large industrial area in southwest Dublin. It was converted from a crossroads (click "1995" on that external link to view the original layout) to an odd sort of roundabout (click "2005") in 2004 to allow the Luas light rail line to pass through the centre.

Grade-separating this junction would be an interesting challenge to say the least. Due to gradient restrictions, the Luas would probably have to pass through at its current level - and therefore so would the Naas Road. Left-turn slips could be provided (and some already are), but the remaining movements - Nangor to Long Mile straight-through and all four right-turns - would probably need to be combined on an overhead roundabout.

There doesn't seem to be a way to have the Naas Road and Luas pass through on a lower or higher level without causing huge disruption. Putting them in a cutting or up on ramps would involve having to sever the Luas at this point for several years. It might be possible to pontoon it elsewhere for the duration, possibly along the northern edge where the buildings are set back, but building and making operational this pontoon would likely be a bigger undertaking than grade separating the junction itself. Therefore, given that the Luas and Naas Road have to remain at-grade, it's the remaining movements that would have to be rebuilt - and presumably undergrounding it would be a non-runner as there is little room for the portals, especially on the Nangor Road. Ideally, more than two levels would be provided for these remaining movements, but this would be a huge and inconvenient structure and could end up an eyesore as both would be above ground. The resulting structure would be more than 12 metres high.

Given all this, it's debatable whether the roundabout would be able to handle the straight-through and all the right-turns. It would have to be signalised. Vehicles would encounter conflicts and dwell times. Nonetheless, it is mapped out below. Note that long ramps would have to lead up to the junction from Nangor and Long Mile roads.

Thinking outside the box, it might be better to facilitate traffic to avoid the junction altogether by creating more opportunities to avoid it nearby. Walkinstown Avenue already allows traffic east of the junction to get between Naas and Long Mile Roads without the junction, and a proposed link between these two points across the Naas Road from Oak Road to Robinhood Road could, if junction ramps were added, provide a similar opportunity for traffic to the south and west of the junction. The Naas southbound to Nangor movement is more difficult to achieve; it can be done using this route, but this is hardly attractive (400 metres longer).

Please give your opinion on this road proposal. Rate it out of 10, and whether you think the standard (road width) is appropriate.