A road project in Perth has become a case study for future Scottish infrastructure projects due its carbon-focused procurement approach. Motorists in Perth, central Scotland often face long queues because the road network directs high volumes of local traffic into the city centre. The River Tay cuts through the town from north to south and can only be crossed by two road bridges in the city centre. Its lack of suitable alternative east to west routes means that drivers cannot avoid using the congested central Perth streets. Congestion led to this part of the city exceeding national air quality standards. As a result, local authority Perth & Kinross Council had to come up with a plan of action. The council is undertaking its biggest ever infrastructure project, the Cross Tay Link Road (CTLR), to tackle the congestion – and resulting air quality – issues. The council’s project officer Sarah Gardner says that the scheme will provide motorists with an alternative route, reducing travel times and “creating capacity in the city’s road network that will enable a shift to green modes of travel”. CTLR involves the construction of a 2.2km realigned dual carriageway on the A9 which skirts the town to the west. It will feature a grade separated junction, roundabouts and a 76m three span overbridge leading to a new bridge across the River Tay. The bridge will be north of the existing ones and will span the Highland Main Line which connects Perth with Inverness. It will be 307m long and 15.7m wide, including a 3m wide footpath and cycle lane. From the eastern abutment a new 5km single carriageway road will be built with connections to the A93 and A94 east of the Tay. A total of four roundabouts will be built along the link road, while a green bridge is being constructed across the route at Hayfield as a crossing for animals and people.
In addition, a New Active Travel Route will be Created Along the Full Length of The CTLR.
The total cost of the work is £150.5M, with £40M provided by the Scottish Government and the rest from the council. Perth & Kinross Council put carbon management at the heart of this project, integrating the PAS 2080 specification for managing whole-life carbon in infrastructure within the procurement of the design and build contract. As a result, Bam Nuttall, which was awarded the contract for the scheme, has reduced CTLR’s carbon footprint by over 35,000t and its cost by £5M. Carbon focus The preferred alignment for CTLR was approved by the council in December 2016. Consultant Sweco then prepared the specimen design, planning application and environmental impact assessment. Efforts to reduce the project’s carbon emissions started as early as the specimen design process, with the implementation of the PAS 2080 principles. The council wanted PAS 2080 compliance to continue, so it incorporated carbon management into the procurement of the design and build contract. Three environmental questions were included in the invitation to tender. The questions were focused on: landscape works execution interface of the works with “sensitive environmental receptors” ways a 14,200t (30%) carbon footprint reduction compared to the specimen design could be delivered. “This approach in our procurement process has been used as a case study by the Scottish Government and will be used in the newly updated PAS 2080 guidance which will be published shortly,” says Perth & Kinross Council roads infrastructure manager Jillian Ferguson. Bam Nuttall was awarded the contract in August 2021 after outlining ways to achieve carbon savings of 26,300t. The client engaged the firm in a year long early contractor involvement (ECI) arrangement to ensure design optimisation. Bam Nuttall project design manager Keith Tully says: “Through that ECI period – which often you wouldn’t have on a design and build job – we had the opportunity to really focus on the design. It gave us time to optimise our design, but also to get our procurement and our construction methodologies in place.”
Bam Nuttall Appointed an Arup And Fairhurst joint.
venture to develop the outline and detailed designs. Through design changes and value engineering CTLR’s carbon footprint decreased by over 35,000t to just under 50,000t. Cement replacement ground granulated blast furnace slag (GGBS) is also being used to further reduce embodied carbon. Bam Nuttall construction manager for CTLR John Slaven says that structural concrete mixes contain 65% GGBS. “Drainage design was made more sustainable with more use of grass surface water channels and deletion of one SuDS [sustainable drainage system] pond,” adds Gardner. Other carbon saving design changes include refinement of the road geometry and roundabout designs and the change of box culverts to pipes where possible. Another way Bam Nuttall slashed CTLR’s carbon footprint is by recycling all of the excavated earth, minimising emissions associated with its transportation. This material will be used to form project features such as road embankments. Slaven is confident that further carbon emissions will be achieved through the use of fuel efficient plant. Progress Construction is progressing across all parts of the project, thanks to the decision to bring earthworks forward to May 2022 instead of winter of the same year. “We broadly completed the bulk earthworks of the scheme by September,” says Slaven. The team is now working on drainage and ducting activities, as well as piling work for the A9 overbridge and River Tay crossing. Construction of the green bridge is progressing and is expected to be completed this summer. Work on junctions and roundabouts has also begun. The link road is expected to be completed by the end of the year and main road infrastructure is expected to be completed in autumn 2024.