The 675m tunnel under the River Shannon is one of the largest and most complex infrastructural projects ever undertaken in Mid-West Ireland.
RPS, in a joint venture with COWI A/S of Denmark, has fulfilled the role of project consultant since 1999, and we have worked with our JV Partner, Limerick City and County Council and Transport Infrastructure Ireland on delivering the southern bypass of Limerick City, from the N18 to the N7; a key piece of infrastructure that forms a critical link in the government’s proposed Atlantic Corridor on the west coast of the country.
We developed the scheme through constraints study, route selection, traffic modelling, tolling studies, preliminary design, EIS, CPO and oral hearing with the granting of permission by An Bord Pleanála in 2004. We then provided technical advice and assistance to the NRA for the tender phase and provided technical advice, design review and contract monitoring services during the construction phase of the project.
The scheme comprises 10km of mainline dual carriageway, four grade separated junctions, 11 major bridges, including two bridges in excess of 100m in length and the tunnel itself. The two largest bridge structures were the N18 Interchange Underbridge (122m) and St. Nessan’s Road Overbridge and reinforced earth structure (115m).
The key element of the preliminary design was the selection of a crossing type for the River Shannon with factors including marine traffic, environmental, engineering and cost considerations. The tunnel was ultimately favoured over low or high level bridge options due to factors including disruption to traffic associated with the opening bridge, the long term environmental benefits of the tunnel and significant public support for the tunnel option.