Limerick Tunnel

RPS, in a joint venture with COWI A/S of Denmark, fulfilled the role of project consultant and worked with Limerick City & County Council and Transport Infrastructure Ireland to deliver the southern bypass of Limerick City. This key piece of infrastructure forms a critical link from the N18 to the N7, part of the Atlantic Corridor on the west coast of the country.

The project 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.

Key details

Project name

Limerick Tunnel


Limerick County Council and Transport Infrastructure Ireland (TII) 



Services provided

  • Project Management
  • Route selection
  • Public consultation
  • Complusory purchase order
  • EIA
  • Site investigation
  • Prelim design
  • Tolling study
  • Safety audit
  • PSDP
  • Oral hearing
  • Specific design
  • PPP Tender
  • Advance archaeology contract
  • Design review & construction


The Limerick Tunnel project is one of the largest and most complex infrastructural projects undertaken in the Mid-West Region of Ireland. The project feasibility report investigated a high-level bridge to allow for ships passing to Limerick port and alternatively an underground tunnel. The tunnel was chosen as it represented the most suitable option for the surrounding environment.

A key challenge on the project was the European Union environmental regulations, as the proposed site was a Special Protection Area for birds (SPA), a Special Area of Conservation (SAC) and a Natural Heritage Area (NHA). This required a comprehensive and on-going monitoring of the River Shannon during the full duration of the project.

The depth, span and ground conditions at the site of the tunnel all proved challenging. The basin has a length of 550 meters and a depth of 9 meters. The soft alluvial soils found at the riverbank added an additional geotechnical complication to this project.  

Limerick Tunnel under construction


Working with partner consultant, COWI, we  developed 10 to 15 preferred route options following extensive investigations, including engineering, economic, geotechnical, environmental studies, traffic studies and public consultation. The route options were chosen with the communities and major existing constraints in mind. These options were reduced to two for public consultation, a high-level bridge and a tunnel.

High and low level bridges, and tunnel options to cross the River Shannon were considered in terms of their effect on a number of issues including: environment, traffic, shipping safety and cost.

We developed the project through constraints study, route selection, traffic modelling, tolling studies, preliminary design, EIS, CPO and oral hearing. With planning permission granted, we provided technical advice and assistance to Transport Infrastructure Ireland for the tender phase and provided technical advice, design review and contract monitoring services during the construction phase of the project.

The final constructed project delivered a 900m immersed tube tunnel under the River Shannon, 10KM of dual carriageway, 10 bridges and 4 underpasses.

Project statistics

Metres immersed tube tunnel
Kilometres of dual carriageway

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