The Cross Tay Link Road Green Bridge

Work is now underway on the Green Bridge element of the Cross Tay Link Road, and with the in-situ concrete foundations and abutments now in place, the pre-cast arches are due to be installed next. It is anticipated that the bridge will be complete by late summer 2023.

Straddling the new Link Road, the Green Bridge will reconnect existing footpaths in the forest plantation at Highfield, Scone.

Green bridges – also referred to as wildlife overpasses – allow woodland mammals and insects safe passage across manmade impediments. The report “Green Bridges – A Literature Review” (NECR181), commissioned by Natural England, identified that green bridges can make an important contribution to sustainability by:

• Creating a safe crossing point for wildlife

• Joining up habitats and connecting colonies

• Providing a home for wildlife

• Creating a crossing point for people

• Facilitating movement of beneficial pollinators

• Integrating roads and railways into the surrounding landscape
  
  

Jillian Ferguson, Project Manager, Perth & Kinross Council, commented, “The environment is at the core of the CTLR project’s aims with long-term benefits including improved air quality, and the easing of traffic congestion and noise pollution, particularly in Perth city centre. Alongside these more obvious gains, minimising the impact of infrastructure on the environment through careful design has always been a key priority and the construction of a green bridge to maintain ecological and pedestrian connectivity is an essential element in delivering on this objective.”

Alan Limerick (right), Senior Site Engineer for BAM Nuttall, explains the engineering – and challenges – behind the Green Bridge.

“Although not a new concept entirely, there are very few green bridges in existence in Scotland and the Highfield one will certainly be one of the longest single-span green bridges on completion. It runs 27.2 metres long and, at its widest point, is 33 metres wide.

“Unusually, it is narrower in the middle than it is at the ends and there is a 2-metre drop between the north and south abutments. Building a bridge on a 6° downhill camber does present additional challenges within the build but, on completion, the slight curve shape together with the Swiss-designed arches from BEBO will offer a striking aesthetic and distinctive feature.

“The reinforced concrete abutments are now in place, with preparatory works for the BEBO arch unit installation also completed - BAM Nuttall partnered with Beattie FRC from Falkirk for these works. The installation of the BEBO arch units will take place during March and this will involve the split arch units being lifted into position simultaneously using two 150-tonne mobile cranes working together.

“The two split arch units are lowered into position and rest against each other at the crown of the arch prior to be the units being stitched together. On completion of installation of the arch units, follow on works will include the construction of a parapet upstand for handrails, waterproofing of the top side of the arch units, drainage works and backfilling over the arch units. Once the structural works have been completed the soft and hard landscaping works will be undertaken to form the safe crossing point for both wildlife and people as well as reconnecting ecology habitats and creating new habitats.”

Sean McLeod, Landscaping Clerk of Works for the project, will oversee the planting and landscaping of the Green Bridge.

“Landscape planting is a significant aspect of the CTLR project and the Green Bridge is one of the major elements of this. The bridge will connect two sides of an existing woodland area at Highfield and in the narrower middle section will offer a 5m-wide footpath and viewing platform, and 14m of greenspace for wildlife to cross. Planting will be undertaken during 2023 and we can expect to see green space emerging almost straight away, and continuing throughout 2024.

“Originally this area was a monoculture of trees, but we have taken the opportunity to expand the biodiversity of the woodland, improving on what was there with a mix of broadleaf trees and conifers. In addition to this, we are creating a wildflower meadow which, as well as being low maintenance, also offers a better environment for bees, bugs and reptiles, and allows small mammals and birds to forage under cover.

“From an ecology point of view, creating a pass for wildlife to go over is always better than the option of tunnels going under. A seamless route across the new Link Road will reconnect the woodland area and allow a safer and more natural environment for our wildlife and give walkers and cyclists using the footpath the opportunity to witness more nature up close.”

Sarah Gardner, CTLR Project Officer at Perth & Kinross Council, added, “We are also working with Scone Estates and the local community to identify and implement additional path links within the woodland area to enhance connectivity for all users. The community will also work with Nichol Wheatley, a local artist, to design and implement waymark signing and and information panel at the new viewing platform.” (See more on page 8).

Wildlife at Highfield

• Red Squirrels

• Deer

• Small Mammals

• Bees and Bugs

• Reptiles

The Scottish Green Infrastructure Forum defines a green bridge as “a structure designed to allow wildlife to cross a manmade impediment, such as a road or railway line.” There are several examples of this kind of green bridge around the world, but very few in the UK and only a handful in Scotland. The Green Bridge at Highfield plays a significant part in the landscape design objectives as laid out by Perth & Kinross Council for this project.