The Preston Western Distributor

Costain, as main contractor for the Preston Western Distributor project, was involved from the earliest stages, thanks to the UK’s Early Contractor Involvement approach. The project was delivered on time and on budget to the benefit of the local environment, local businesses and the region’s workforce. David Arminas reports*
September 7, 2023
Junction 2 on the M55 motorway, connecting with Edith Rigby Way
Junction 2 on the M55 motorway, connecting with Edith Rigby Way

The €239.6 million Preston Western Distributor is the first major bypass to be constructed in the area since the Preston Bypass on the east side of Preston, a city in the northern English county of Lancashire. After seven years of planning and construction, from 2016 to earlier this year, the project is now open and stands as an example of best practice for setting up and running a partnership agreement - with much done against the recent backdrop of COVID-19 pandemic restrictions.

“Costain played a vital part in the development, design and construction process for the Preston Western Distributor project from the start of their involvement in 2016,” said Phill Wilson, project manager with the client Lancashire County Council. “This project has been an excellent example of how finding the right partner though the Early Contractor Involvement process can produce the cooperative team necessary for such a complex and challenging project.”

In the traditional design–bid–build contract, the contractor is engaged only at the end of the design phase. But in the Early Contractor Involvement (ECI) contract model, the principal contractor is engaged at an early stage in a project to offer input into the design phase and suggest value engineering changes. Studies have shown that savings of around 10% in construction time and 7% in cost are achievable. The ECI model has increasingly been used in the UK since the early 2000s and is gaining support in Australia and New Zealand. Costain is, in fact, no stranger to the ECI phases of capital investment programmes in both natural resources and transportation sectors. The contractor says that ECI engagement is critical to transforming the performance of new infrastructure, during both the construction phase and subsequent live operation. Key ECI benefits to the contractor and client on the Preston project include:

• The Early Contractor Involvement phase was delivered on time and under the forecast budget. Meanwhile, the construction phase concluded on time and on budget;
• Accolades for the contractor’s and overall project’s scorecard when it came to social and environmental benefits;
• Just over half - 55% - of employees, including from the supply chain - came from the local area, with 10 apprentices from local colleges employed on the programme;
• Costain innovated to save the equivalent of 6,134tonnes of CO2 emissions during construction, saving almost €8.2 million;
• The project delivered a 9.04% biodiversity net gain for habitats and a 10.81% net gain for hedgerows.

COVID-19 restrictions presented unforeseen challenges, not least high levels of anxiety as people feared for friends and family. Costain says it sought to create an environment onsite which provided support to all employees and safeguard their wellbeing, such as offering Mental Health First Aid Training. The company worked with various charities to counter the stigma of mental health issues affecting men and encouraging those who needed support to access counselling through Costain’s Employee Assistance Service.

As with many contractors during COVID-19, Costain put in place a range of new ways of working to ensure compliance with mask-wearing, social distancing and one-way systems around site offices. It created an app which allowed members of the team to report any concerns they had so that they could be addressed immediately. A rota was implemented to ensure that only those needed onsite were there and rather than having one hub office location, employees were distributed across three project offices. The offices were fitted with physical barriers between individuals. Costain believes that the measures helped ensure that no cases of COVID-19 transmission were reported on the project.

Early involvement

The city of Preston, on the River Ribble, is the administrative centre of the county of Lancashire. It  has a population of 114,300; Preston and its region have a population of round 315,000. The 13.3km-long original Preston Bypass was opened in 1958 as the UK’s first ever stretch of motorway – a year ahead of the official opening of the first of four sections of the north-south M1 motorway, which was to be the UK’s first full-length motorway at 311km. The early M1 had no speed limits, crash barriers and lighting; it also had soft rather than hard shoulders.

Today, the Preston Bypass forms part of the M6 motorway. Meanwhile, the new Western Distributor Bypass flows to the west of the city. It was funded through the Preston, South Ribble and Lancashire City Deal, which aims to improve people’s lives by providing much needed additional capacity on a heavily congested section of Preston’s local road network (see box, Preston: the big picture).

The new project’s flagship is the 4km Edith Rigby Way, a dual carriageway that links Preston and the southern Fylde area to the M55 motorway via the A583. The scheme also includes construction of a motorway junction and two link roads giving residential areas in the northwest Preston area access to Edith Rigby Way (see box, Western Distributor details).

The Early Contractor Involvement phase began in 2016, three years before construction started. This gave the client,  Lancashire County Council, cost and programme certainty by providing services such as commercial management, value engineering advice, planning and project controls and stakeholder engagement. It also ensured the scheme moved from concept to a buildable project that gained planning consent.  

Costain proactively facilitated a collaborative programme of engagement between organisations and stakeholders to accelerate and assure delivery of the construction phase. The contractor involved statutory undertakers in the planning process, including Network Rail, National Highways (then called Highways England), the Environment Agency and relevant third parties, such as the train operating companies serving the Preston-to-Blackpool line and utilities providers. During the planning process and application, the team engaged with the community and road users at public consultation, providing detailed information about the plans for the scheme and the opportunity for feedback.

Costain developed a dynamic programme plan based on engineering data about the structures, materials and environment, which allowed the company to forecast progress, identify interdependencies and expenditure on a monthly basis. It also allowed Costain to ensure the construction phase was delivered to budget by identifying potential challenges in delivery and enabling a planned, proactive response.  

Costain’s approach to the environment encapsulates this way of working: the required licences from the government’s Natural England agency – responsible for ensuring improvements to England’s ecology - were put in place during the Early Contractor phase, enabling surveys to start ahead of the formal start of construction, without the need to wait for the next ecological season. This saved between three and six months on the programme and enabled highly critical third-party access to the site.

The city of Preston, on the River Ribble, is the administrative centre of Lancashire © Shahid Khan |
The city of Preston, on the River Ribble, is the administrative centre of Lancashire © Shahid Khan |

Complex engineering

The contractor deployed innovative engineering techniques to ensure that it delivered on time and on budget, despite the complexities of the project. Construction of the 278m-long Savick Viaduct is a key example of this approach. The rest of the programme was dependent on the team delivering this significant milestone on schedule – despite it spanning a brook and a floodplain with power cables close by.

To ensure the milestone was met on time, Costain worked closely with a specialist supplier to devise the most efficient way of installing the steel beams used to build the Savick Viaduct. Costain carried out as much preparatory work as possible offsite, such as the permanent formwork and falsework, processes which strengthen the load-bearing capabilities of the beams. The beams were then moved into position using self-propelled modular transport and finally lifted into place. This saved €1.18 million and significantly reduced the amount of time which engineers spent in safety-critical environments.

The ground conditions across the project were technically challenging. At Savick Viaduct, Costain had to carry out extensive additional temporary works, such as installing working platforms and deploying vacuum drainage solutions to stabilise the ground before beginning the main works. This required extensive stakeholder engagement, including with the Environment Agency. This process allowed the contractor to stabilise the ground conditions sufficiently to drive the piling 40m beneath the surface.

Another prominent example of the project’s complexity is the Lea Viaduct which spans the electrified Preston-to-Blackpool railway line as well as a canal. In this case, Costain’s in-house survey team used 3D modelling techniques and geotechnical analysis to model the effect of the planned works on the railway and the overhead line equipment. The team successfully demonstrated that any forecast ground movement due to the planned works would remain within acceptable limits.

This complex engineering project also required integration with existing transport and utilities infrastructure. Costain’s solutions minimised disruption to the travelling public, while reducing time, cost and risk associated with the works. Over the two nighttime motorway closures in June 2021, the contractor installed the 130tonne, 48m-long Becconsall Bridge over the M55, enhancing local connectivity by creating a brand new junction.

More than 6,800m³ of Leca lightweight aggregate (LWA) fill (10-20mm), from materials supplier Saint-Gobain, was specified for both ends of the Becconsall Bridge’s abutment sections to provide a sustainable lightweight solution with robust stability over delicate ground conditions. The delivery took place without the need for any road closures of the M55 (see box, Leca).

At Savick Viaduct, two large sewers servicing northwest Preston passed beneath the area identified for this new structure. Vibration monitoring surveys were conducted to ensure mitigation of any risk to these assets appropriately ahead of construction through the detailed design and enabling works. During construction, Costain used reinforced concrete slabs onsite.

Working closely with Network Rail, the concrete supplier and temporary works designers, Costain used a ‘production thinking’ approach to deliver all enabling works for the 233m-long Lea Viaduct offsite and lift the new structure into place once in situ. Agreed planned closures of the railway took place on Christmas Day and Boxing Day, 2020.

Biodiversity net gain

Operating in sympathy with the environment was a critical priority for Costain, working hard to improve biodiversity and reduce carbon emissions from the project. The landscape plans for the scheme were designed to restore farmland and to protect and enhance habitats for species including great crested newts, bats, birds, brown hare, hedgehogs and common toads. Costain designed the landscape to create a 9.04% net gain for habitats and a 10.81% net gain for hedgerows.

Early Contractor Involvement allows input from construction contractors to feed developers information that will allow them meet their legal biodiversity net gain requirements. According to the consultancy Ecology by Design** - a member of the UK’s Chartered Institute of Ecology and Environmental Management - biodiversity net gain is a process of biodiversity offsetting, meaning habitat loss caused by a new development is mitigated to ensure an overall increase in biodiversity post-development.

To establish the best way to protect the habitats onsite, a metric is used. A development must show evidence that a development will increase the biodiversity value of a site by at least 10%. This statistic is presented in the value of a biodiversity net gain metric called ‘biodiversity units’. If habitats and ecological value cannot be added to the site itself, then mitigation plans must be put into place to ensure habitats. This can be achieved either by enhancing the onsite biodiversity or creating new habitats elsewhere.

During the earthworks, 600,000m³ of subsoil and topsoil were removed. But rather than shifting this material from site and causing significant congestion to the local road network,  100% of the earth was kept onsite. Working with the client, Lancaster County Council, Costain remodelled the landscape with all earth relocated to the roadside where it has been replanted with trees and serves both as a visual point of interest and as a noise barrier. This approach removed 20,000 journeys of 96.5km each from the local road network.  

The project used 100% renewable electricity to power onsite works. However, Costain also explored other sources of clean energy, such as hydrotreated vegetable oil (HVO) and the use of hydrogen. This included working with hydrogen start-up Hydrologiq to trial the use of a hydrogen-powered fuel cell generator at the M55 compound. Together, contractor and supplier demonstrated that green hydrogen would remove almost all carbon emissions associated with onsite operations (see box, Hydrologiq generator).

Meanwhile, telematics data from onsite machinery was analysed to identify opportunities for reducing plant idling. Working in close step with the supply chain, plant idling fell by around 20%. Diesel usage was eliminated across the project, replaced with HVO fuel manufactured from sustainable, renewable feedstocks.

Social value

Costain’s approach to social value was grounded in the desire to maximise the value of work placed with local businesses and for local people. The project team ensured that the local economy benefitted from the investment in the project in several ways. One way was the awarding of work to companies in the local supply chain wherever possible. In the end, 45% of the project spend was invested within a 40km radius of the site, with an additional 37% spent up to 160km. Importantly, recruitment took place extensively from the local area, with 58% of the workforce based in the community.

As part of Costain’s Lancashire Skills Pledge, the contractor supported Preston College’s T-Levels programme. A T-Level is a UK nationally-recognised qualification for 16 to 19-year-olds that takes two years to complete. A T-Level student will typically spend 80% of their time in the classroom and 20% on a minimum nine-week placement with an employer, in this case with Costain.

Costain also worked with local schools to engage students with the potential of a STEM – science, technology, engineering and mathematics - career. The company took on 10 apprentices throughout the project, creating early career opportunities in engineering and construction. n

*The main material for this article was kindly supplied by Costain.

**Ecology by Design: 


Project Details

Construction consisted of:
• A new motorway junction: the M55 Junction 2, comprising four slip roads, one bridge crossing the motorway and two roundabouts giving access to the west of Preston; 
• Three new roads: Edith Rigby Way dual carriageway (4km), the William Young Way East-West link Road (3.2km) and the Avice Pimlett Way Cottam Link Road (0.6km);
• Three underpasses; 
• Two viaducts; 
• Bartle Lane overbridge.


Leca lightweight aggregate fill

Leca LWA has been used extensively in structural and geotechnical projects for over 60 years. For road embankments, Leca LWA exerts much lower horizontal earth pressures compared with other backfill materials; it helps improve stability and reduces the need for counterfill. It has an installed bulk density of around 20% of that of general fill materials and will considerably reduce settlement of the road or rail carriageway, both immediately and in the long term.

Primary properties include 75% reduction of horizontal earth pressure to retaining structures; superb insulating and free drainage properties; is resistant to extreme temperatures, moisture and chemical attack;and is 100% inert - containing no harmful substances or gases.

Compaction of Leca LWA requires substantially less compaction effort when compared to conventional fills including Type 1 Fill and GSB Type Fill.  The company says that a  value adding property “unique to Leca LWA”, is the ability for vehicles to continue operations over the placed material without the risk of potential surface crushing. It can be placed in the same way as other conventional aggregates, either by tipping and spreading using a tracked dozer or tracked excavator.

Compaction can be done using a vibrating plate compactor with a maximum ground bearing pressure of 50kN/m².  Compaction is expected to provide a reduction in volume of 8-12% with the average being around 10%.