The N7 has always been the busiest road in Ireland. Even as far back as the 1960s, there were traffic problems passing through Naas, the first large town heading southwest out of Dublin. Since the N7 is the starting point of the route leading to the three regional cities of Limerick, Cork and Waterford, it is one of the most important strategic routes in the country.
Back in the 1960s, widening of the road between Dublin and Naas was undertaken to basic dual carriageway. This was a time of very low capital spending and roads were not a high priority, with traffic volumes generally being very low nationwide and economic growth so low. As a result, it apparently took around 10 years for the widening to be completed from the Long Mile Road area in Dublin as far as the outskirts of Naas.
As time passed, the M50 Dublin ring road was completed and the N7 corridor in and near Dublin became increasingly densely developed. The council instituted a number of improvements along the M50-Rathcoole corridor in particular in a piecemeal fashion which closed local access, added grade-separated junctions and widened a limited amount to 6 lanes. In August 2006, a much-needed project was finally completed after only 18 months construction. The remainder of the road from Rathcoole to the start of the Naas bypass was widened to 6 lanes with most local access closed off and several grade separated junctions added.
Back in the 70s, with tailbacks coming out of Naas in both directions during times of heavier than normal traffic, it was obvious by the 1970s that the town would need a bypass, and a big one too. Things moved slowly though, so it wasn't until the end of the decade that work finally began, taking several years. Back then, and indeed until relatively recently, it was common in Ireland for funding for transport projects to be assigned on a year-by-year basis, meaning that the local council could be left out of pocket the following year and unable to pay the builders. If this happened, work simply stopped until the money came back. This meant that works often took an unusual time to complete. Work started on the bypass and it took three years to build, though it was only 7 km. With motorway restrictions, it was the first motorway in the country. RTE have some archive footage and an article covering the road opening.
The traffic problems immediatelyshifted a few miles down the road to the town of Newbridge, which became the next focus of investment. The dualled section was extended a little further from the Naas Bypass as far as the outskirts of the town. A decade later, in June 1993, a large Y-shaped motorway was ready to take the traffic further southwest before forking south towards Waterford and southwestpast Newbridge and a little further towards Limerick and Cork.
The southern fork was named the M9 and marked the new starting point of the N9 Naas-Waterford trunk route.
With a short dual carriageway extension, the route continued towards Kildare, main town in the eponymous county. This town spent literally decades trying to get its bypass, which was finally completed in December 2003. It was a expensive (€160M) and environmentally difficult twelve kilometres to build, as a wetlands, the Pollardstown fen, was threatened by it - the road was to run in a cutting below the level of the surrounding land, which would have resulted in the wetlands draining into the road unless remedial action was taken. In the end, a Dutch method known as "tanking" was employed whereby the road cutting was lined with plastic sheeting which was covered over afterwards, sealing the road off from its surroundings.
The next town in the chain of hamlets stretching all along the N7 is Monasterevin. Its bypass arrived in November 2004, less than a year after the previous section had opened. Following the same distance again is the large midlands town of Portlaoise, which marks the point at which the route forks again in the same way: southwest continues to Limerick, while there is a southbound road taking it on the long journey to Cork. When the motorway bypass opened, the start of the N8 was transferred to a new junction on the Abbeyleix Road.
The N7 continued as a single carriageway onwards through some villages like Mountrath and the oddly titled Borris-in-Ossory, before finding itself in Roscrea, one of the many towns that had been fighting for a bypass since the early 1980s. It got its wish when this section was replaced by the M7 right at the end of December 2010.
The next large town is Nenagh, which got a bypass earlier than many towns along the route - in 2000 - but it was only a single carriageway running in a wide arc along the southern outskirts. This bypass was upgraded to a motorway as part of a project which included an extension the rest of the way to Limerick. The bypass section opened fully in December 2009 with the remaining two parts following in April and September 2010. The old route made its way down further west, only pausing for breath in Birdhill.
The reason the original Nenagh Bypass was only single-carriageway is demonstrative of the evolution in thinking that took place from the 1990s to the 2000s. The fact that traffic was going to rise inexorably from background levels to a full tidal wave as a result of rapid economic growth was lost on the government until quite late in the day. The bypass was in planning from the early 90s, a time when it was still fully intended to only create motorways from Dublin out to the border (M1), Kinnegad (M4) and Portlaoise (M7). All other roads would only be given single carriageway treatment. It just wasn't thought that anything more would be needed in the next 30 or more years. By the time the Nenagh Bypass opened in 2000, the Celtic Tiger period of rapid economic growth had been going on for nearly 10 years, and all trunk routes in the country were bursting at the seams, with traffic growth of 10% a year commonplace in many areas. Finally, in 1999, it was acknowledged that nothing less than dual carriageways, or motorways, would suffice for the nation's arteries. Of course, this rendered Nenagh's relief road defunct before it was even completed.
The first phase of a ring road snakes its way around Limerick to the south and opened in May 2004. It was redesignated a motorway in 2009. The second and final phase, which was initially to be the final part of the N7 but opened as N18 instead, started in October 2006 and opened in June 2010. It was an expensive (€360M) and complex project as it involved submerging twin road tunnels under the mighty Shannon, the longest river in Ireland. This second phase of the Limerick ring road wasn't classified as a motorway just yet, however. This may have to wait for a subsequent round of upgrades.
By end 2010, the M7 was complete. There were now only two more major schemes. The first was the construction of the grade separation of the Naas, Belgard and Fonthill Roads at a location called Newlands Cross. This took place between 2013-2015, opening in May. It did not, however, constitute a new section of motorway, as the N7 Naas Road is dual carriageway only at this point.
The second was widening of the motorway from Naas to the M7/M9 split east of Newbridge, which started in January 2018 and was completed in August 2019. This also included a new junction 9A at Osberstown, north of Naas, and a western bypass of Sallins. Additionally, junction 10 was entirely reconstructed, and connected with a different road.
There is a long-range plan to convert the non-motorway part of the N7 between the M50 and Naas to motorway. No timeframe is announced, but preliminary design is taking place. The part of the road west of Kill is already good enough, but parallel local roads would be needed between Kill and Rathcoole and some junctions built in 2006 along there would need to be enlarged.
The Naas-Newbridge widening and junction rebuilds will all be done by the end of the year.
The widening is complete, but there is still no end date for the new junctions.
Junction 10 was completed some months ago. New junction 9A and the Sallins bypass are due to be complete by the end of this year.
Junction 9A and the Sallins bypass will not open until the summer. The contractors are having to redo some work.
Junction 9A Osberstown and the Sallins bypass are now fully open to traffic.