Highways Design: Enhancing connectivity and safety

• Realignment of a 2km stretch of the A9 dual carriageway trunk road, with a new grade-separated junction.
• Creation of a new 6km single carriageway link road extending from the A9 to the A94, connecting to the local road network with four at-grade roundabouts.
• Integration of 12km of new or upgraded paths, mainly shared use for pedestrians and cyclists, ensuring safer, more accessible routes for non-motorised users.
• Development of a ‘Park & Choose’ concept utilising the redundant carriageway of a section of the old A9, reducing excavation waste, and providing a resource where visitors can park on the edge of the city and utilise the path network to access areas around Perth.

From the outset, Sweco’s highways design experts married the importance of improving connectivity with the need to minimise disruption to local communities. The design of the new road network carefully balances capacity and safety, ensuring smoother traffic flow while supporting Perth’s long-term growth.

Our team developed preliminary and specimen designs for the road network, addressing key congestion points and improving accessibility. This included the realignment of a 2km stretch of the A9 trunk road dual carriageway, complete with a new grade-separated junction.

In addition, a 6km single carriageway link road now extends from the A9 to the A94, linking to the local road network with four at-grade roundabouts. To further promote sustainable and active travel, the scheme features 12km of new or upgraded, mostly shared-use pedestrian and cycle paths to ensure safer, more accessible walking, wheeling and cycling routes.

Sweco quickly established themselves as a key asset in the Cross Tay Link Road project, both in terms of developing an innovative and ground-breaking approach to sustainable design and procurement, and in assisting us with the inevitable challenges that arose as we moved the project forward. They proved to be a trustworthy and efficient resource within the project team, ensuring that this important milestone project within the Perth Transport Futures strategy delivered on our objectives for the surrounding communities and all key stakeholders involved.

Jillian Ferguson, Roads Infrastructure Manager, Perth & Kinross Council

Civil Structures: Engineering complex crossings

• The 307m long, three-span Destiny Bridge crossing the Highland Mainline Railway, the River Tay, and the surrounding floodplain.
• The Highfield ‘Green’ Bridge, designed to maintain wildlife corridors and paths through Highfield Woods.
• A new grade-separated junction crossing the realigned A9.
• Engineering infrastructure that seamlessly integrates with the natural environment is no mean feat, but Sweco’s bridge engineering teams rose to the challenge with ingenuity and precision.

Central to the project is the Destiny Bridge – a remarkable 307.4m long, three-span structure that gracefully crosses the Highland Mainline Railway, the River Tay, and the surrounding floodplain. This complex crossing required meticulous planning and collaboration with Network Rail and SEPA (Scottish Environmental Protection Agency) to ensure minimal disruption and visual and environmental impact.

Another standout feature is the Highfield ‘Green’ Bridge, an innovative overbridge designed to preserve wildlife corridors and paths through Highfield Woods whilst providing segregation of the two to ensure minimal disturbance to local fauna.

This structure exemplifies Sweco’s nature-positive commitment to balancing transportation infrastructure needs with ecological preservation – a cornerstone of its commitment to drive the Green Transition across its multi-disciplinary services.

Landscape Architecture: Preserving natural beauty

• Development of a full Landscape & Visual Impact Assessment inputting to the Digital Environmental Impact Assessment.
• Creation of verified photomontage visualisations to assess and mitigate visual impact.
• Detailed landscape design to seamlessly integrate the road and bridges – including the impressive Highfield ‘Green Bridge’ – into the natural environment.
• Integration of compensatory planting to enhance biodiversity and support wildlife habitats.
• Preservation of key views and landscapes associated with the nationally recognised ‘Garden and Designed Landscape’ of Scone Palace.
• Detailed design amalgamating 3nr SuDS basins into a single wetland habitat providing a significant biodiversity and recreation resource.

The CTLR’s location near Scone Palace, within a nationally recognised ‘Garden and Designed Landscape,’ presented a unique and complex challenge: enhancing infrastructure while preserving the region’s natural beauty and historic landscape.

Sweco’s landscape architects approached this task with sensitivity and creativity, conducting a full Landscape and Visual Impact Assessment to understand and mitigate the road’s visual impact.

The team developed verified photomontage visualisations, allowing stakeholders to preview the design’s integration with the landscape. Detailed landscape design followed, incorporating compensatory planting, Sustainable Urban Drainage Systems (SuDS) and wetlands that not only manage water but enrich biodiversity and blend the infrastructure harmoniously with its surroundings.

Environmental Consultancy: Minimising ecological impact

• Preservation of connectivity for species such as red squirrels, pine martens, and badgers.
• Integration of Sustainable Drainage Systems (SuDS) and wetlands to protect water quality and mitigate flood risks while enhancing biodiversity.
• Wildlife corridors across the Highfield ‘Green’ Bridge

Safeguarding the environment was at the heart of Sweco’s approach to the CTLR project. Understanding the ecological significance of the area, Sweco’s environmental consultants undertook comprehensive surveys to identify wildlife habitats and movement patterns.

Specialist video surveys revealed the need to preserve connectivity for species such as red squirrels, pine martens, and badgers. In response, Sweco integrated measures like the Highfield ‘Green’ Bridge to maintain vital wildlife corridors.

Additionally, the team conducted thorough flood risk assessments and implemented SuDS to protect water quality and mitigate potential flooding risks, ensuring the project not only minimised its ecological footprint but actively contributed to enhancing local biodiversity.

The creation of the Highfield ‘Green’ Bridge in particular exemplifies this commitment, providing a safe passage for animals across the road, while new compensatory planting and wetland habitat features enhance biodiversity. Sweco’s careful integration of ecological considerations into the design means the CTLR not only connects communities but also ‘nurtures nature’ in the local ecosystem.

Carbon Advisory: Setting PAS 2080 best practices for low-carbon design

• Contribution to carbon reduction during design through value engineering.
• A procurement process that incentivised contractors to propose additional carbon savings.

From the project’s inception, Sweco championed sustainability, embedding carbon management into every stage of the CTLR. Working with Perth & Kinross Council, the team embraced PAS 2080 principles, identifying carbon hotspots early in the design phase and proactively seeking solutions. Carbon reduction was woven into procurement, with contractors challenged to propose further savings.

The Cross Tay Link Road is a featured case study in the latest PAS 2080 guidance document from the Institution of Civil Engineers, and is also showcased as a best practice case study in the ‘Accelerating the Decarbonisation of Scotland’s Infrastructure’ report from ICE Scotland.

Flood Risk Assessment and Fluvial Modelling: Ensuring safety and compliance

Highlights:

• Comprehensive hydraulic modelling of the River Tay, Cramock Burn, Bertha Loch Burn and Broxy Kennels Drain to assess flood risk.
• Hydrological assessment to obtain flows to input hydraulic modelling.
• Production of Flood Risk Assessment Report investigating all forms of flooding to the CTLR.

The CTLR project required a thorough understanding of the existing flood risks associated with multiple watercourses in the area. Sweco’s flood risk team conducted extensive fluvial modelling to evaluate the impact of the new infrastructure on flooding to the area and to ensure compliance with Scottish Planning Policy.

Preliminary modelling indicated that the majority of the works would result in a negligible impact on flood risk, whilst in certain sections, proactive flood mitigation strategies were crafted and then successfully endorsed by SEPA and Perth and Kinross Council. The flood risk team played a key role in the design of the CTLR to incorporate the necessary freeboard allowances and compensatory storage to mitigate any potential flood risks, ensuring the safety of the infrastructure and surrounding areas.