Roadbridge on track for early delivery of N4 Collooney to Castlebaldwin Road Scheme

The completion of the N4 Collooney to Castlebaldwin Road Scheme will open another section of the north west to the rest of the country, as well as removing a fatal accident blackspot in Co Sligo.

A core priority under Project Ireland 2040 and the National Planning Framework is the requirement to enhance and upgrade accessibility between urban centres of population and their regions, in parallel with the initiation of compact growth of urban centres. This has a crucial role in maximising the growth potential of regional urban centres, one of which is Sligo, and the economy as a whole.

Project background

The N4 Collooney to Castlebaldwin Road Scheme was included as part of the Building on Recovery: Infrastructure and Capital Investment Capital Plan 2016-2021, as it was identified as a key priority in the roads programme to support economic growth and one of the critical gaps in the existing infrastructure that needs to be upgraded.

The delivery of the N4 Collooney to Castlebaldwin Scheme is listed as one of the key schemes to be delivered under Strategic Outcome No 2 of the ‘Enhanced Regional Accessibility’ of the National Development Plan (NDP).

This section of the N4 has been an accident blackspot for decades, and this was another critical issue that drove the necessity for upgrade works.

When completed, the N4 Collooney to Castlebaldwin Road Scheme will significantly improve safety by reducing fatalities and injuries on the N4 and the surrounding local road network. It will reduce inter-urban journey times and improve journey time reliability, removing barriers to the economic development of the region. Furthermore, it will encourage and support investment and employment in Sligo and the north west.

The contract

The Public Works Contract for Civil Engineering Works Designed by the Contractor for the Design & Build of the scheme was awarded by Sligo County Council to Roadbridge in January 2019.

The project period was planned to run for 32 months, from January 2019 to July 2021. However, Covid-19 impacted this plan, and the works were extended to be completed in Q4 2021. Roadbridge is now on course to complete the project three months ahead of schedule.

The brief

The N4 Collooney to Castlebaldwin Road Scheme brief called for the realignment of approximately 14.71km of the N4 in Co Sligo, 13.82km of which consists of type 2 dual carriageway commencing at the existing N4/N17 roundabout in the townland of Collooney/Toberbride and extending to a roundabout in the townland of Castlebaldwin.

The brief for the comprehensive works included:

–  12.12km of offline realignment from Doorly Road to Cloghoge Lower Road

– 2.58km of widening and improvement of the existing N4 single carriageway to a type 2 dual carriageway

– Major earthworks, including excavation of 700,000 sq m of peat and silts

– New side roads and upgrading of existing local roads

– One compact grade-separated junction on the mainline (Drumfin/Cloonlurg Junction)

– One at-grade roundabout junction on the mainline (Castlebaldwin Junction)

– Three roundabout junctions on sideroads

– Six road underbridges, four road overbridges, and two river bridges

– Culverts and associated diversions of existing minor watercourses and drainage ditches

– All necessary drainage works, diversion of services and utilities, environmental mitigation works and accommodation tracks.

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The works

Roadbridge project manager Brian Snow says that the brief was to upgrade this treacherous section of road, which had over 30 fatalities in the past 40 years.

“The original carriageway had varying carriageway widths and cross-sections, over 70 private accesses and 24 junctions and provided limited opportunity for safe overtaking.

“The project comprises 14.7km of new carriageway between the dual carriageway at Collooney and the Curlew By-pass, south of Castlebaldwin village. It consists of a 2.7km upgrade of the existing single carriageway to a type 2 dual carriageway from the N4/ N17 roundabout to Doorly, 11.2km of offline type 2 dual carriageway between Doorly and the Castlebaldwin roundabout, and 0.8km of offline type 1 single carriageway to tie in with the existing N4 at the end of the Curlews By-pass. There is also 4.5km of type 3 single carriageway and 4.1km of new combined footway included in the scheme.”

The construction work included 12 bridges and a number of ancillary structures, as well as environmental barriers, culverts and gantry foundations.

“The overbridges were all three-span integral bridges constructed using W9 precast beams and in-situ concrete decks. The intermediate supports are columns on ground-bearing foundations, and abutments were high-level bank seats on ground-bearing foundations.”

The underbridges were constructed using precast box structures, with spans of approximately 7.6 metres. Lengths varied based on the skew of the road traversing under the mainline.”

Banagher Precast Concrete supplied precast beams for the bridges, and Shay Murtagh Precast and Croom Concrete supplied the culverts.

Covid-19 impacts

Brian Snow says that all was going well with the project schedule until Covid-19 shut down the country in March 2020. Roadbridge reacted quickly to get sites reopened. In addition to introducing the CIF Covid Pandemic Standard Operating Procedure (SOP), it brought in additional practices and procedures specific to the site, which at first was logistically challenging, but with buy-in from the on-site teams as well as the client and other stakeholders, the project was able to get back up and running with a new schedule.

“There were many challenges faced during the course of constructing the N4 project,” Brian Snow explains. “The most high profile unforeseen one was addressing the impact of the pandemic. However, the policies and procedures that we developed and implemented on site to protect our workforce were well received by the Health and Safety Authority (HSA), Transport Infrastructure Ireland (TII) and our client Sligo County Council.

“As was standard procedure before the pandemic, we held large daily group pre-task talks on all Roadbridge sites. Under the new Covid-19 SOP, we broke our workforce into small pods of workers who operated together and didn’t mix with other pods. Under the new measures, instead of one overall group task talk, we had talks with smaller distanced groups. The pod set-up also came into play for breaks, with pods taking staggered lunch breaks, etc.

“It was difficult. But we learned quickly. This was helped by everyone engaging in the process and quickly understanding what they had to do to protect themselves and their fellow workers.”

Managing excavated materials

Another major challenge was managing over 1.1 million cubic metres of unsuitable material that required excavation to construct the road embankments.

“We were able to manage the unsuitable material and dispose of it within the land made available (LMA). This greatly reduced the carbon footprint of the project by avoiding disposal of material in off-site licensed pits.”

Brian Snow adds that the weather in the north west has always been a major obstacle for any civil engineering contractor and this N4 project was no different.

“Civils schemes in the north west of Ireland always have to be prepared for difficult weather conditions. But we are well used to dealing with this, as Roadbridge has a long history of civils works along the west coast of the country.”

Project outcomes

Brian Snow says that the project has gone well despite Covid-19 and other challenges.

“We are ahead of schedule. The new road should be ready for use later this summer.

“Covid-19 has changed forever how we approach our work. What was at first an enormous hurdle was addressed with ingenuity and determination.

“The end result of the project will mean safer and quicker journeys on this section of the N4. It also marks the completion of the N4 route, opening up the north west to the east of the country. So, it is a project that we are very proud to have delivered,” Brian Snow concludes.

Other Roadbridge projects

The N4 Collooney to Castlebaldwin Road Scheme is a prime example of a traditional Roadbridge roads project.

As well as the N4, Roadbridge is currently finishing the new North Runway at Dublin Airport, another project which was deemed essential during the pandemic.

Marine works have become a significant area of focus for the firm in the past few years, mainly due to the impact of Brexit. Roadbridge is the framework contractor to Dublin Port Company and is involved in major marine developments in Scotland.

Roadbridge’s overall portfolio of works includes aviation, gas, industrial/ commercial, marine, rail, roads, water and wind projects. Its order book is secured for the next three years. The future is bright with similar projects to the N4, including N5 Ballaghaderreen Bypass, the Coonagh to Knockalisheen Northern Distributor Road in Limerick, and the A465 PPP Motorway Project in Wales secured over the past 12 months.

The contractor has also commenced works in other sectors in Ireland, the UK and Sweden.


In 2020, Roadbridge introduced its “YourSustainabalePath” initiative to promote and drive its sustainability ambitions. This was introduced on the N4 project and became a resounding success. The initiative focuses on five pillars across the company. These are ‘Water Protection’, ‘Waste Reduction’, ‘Biodiversity & Habitat Protection’, ‘Air Quality Protection’ and Energy Efficiency’.

Ivan Conway, Quality & Environmental Manager, Roadbridge, is leading the programme, which he says has had full employee buy-in.

“We are delighted with how the initiative has been embraced across the company. There is a strong appetite to build sustainably and reduce emissions.”

Accredited to the ISO 50001:2018 Energy Management System, Roadbridge’s main energy consumer remains plant and fleet.

“Through a focused plan led by our plant department, we have achieved a 4% decrease in our carbon emissions across the business, resulting in the direct prevention of 1,200 tons of carbon from being produced. This was achieved by updating 22% of our plant and fleet to more efficient engine models in 2020 and the introduction of hybrid plant and electric vehicles to our fleet. We also provided training on the more efficient use of plant and vehicles, which was fundamental to the success of the initiative,” Ivan Conway concludes.

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