BREEAM Infrastructure rates A30 expansion work as Very Good

The A30 Temple to Higher Carblake Improvement was a £60 million highway improvement scheme part funded by Cornwall Council and the Department for Transport.

The A30 trunk road between Temple and Higher Carblake is a 4.5-kilometre section of single carriageway and at peak times the capacity of this section forms a serious constraint to traffic flow on the A30. This has a detrimental effect on the Cornish economy and the often severe congestion leads to poor journey time reliability, driver frustration, conflict and collisions.

The proposal sought to merge into the existing landscape, mitigate potential impacts, and where possible, enhance the existing roadside landscape. This included replicating local variations of Cornish hedging, turved mounds seen adjacent to the lanes running through the North Bodmin Moor SSSI and also using large stones in particular areas to reflect the Tors common at the eastern end of the proposal. In addition to this, new boundary stones were proposed to mark the Area of Outstanding Natural Beauty.

The following lengths of hedge/planting were included:

• 3.62 kilometres of new Cornish hedges with hedgerow

• 1.77 kilometres of new Cornish hedge

• 1.41 hectares of new woodland and scrub

• 0.40 kilometres of new native hedges

Parts of the scheme lay within an Area of Outstanding Natural Beauty, an Area of Great Landscape Value and an Area of Historic Landscape Value. The site crossed a Site of Special Scientific Interest, was adjacent to a number of County Wildlife Sites and the River Camel Special Area for Conservation is approximately 2 km from the site.

The greatest challenge during the design stage was to create an alignment which minimised land take and minimised the impact on the many constraints along the length of the route, all whilst meeting the necessary design safety standards.

Widening and realigning the carriageway

This scheme upgraded the single carriageway to a dual carriageway standard through widening and realigning the existing carriageway to provide additional lanes, central reservation and verges. To improve safety and accommodate the new alignment the scheme included the construction of three new overpass bridge structures to replace the existing at-grade crossings.

Safe passage of protected species

A number of European protected species were identified within the vicinity of the scheme including otter, dormouse and species of bat. A large multi-species culvert was strategically placed to allow safe passage of otter, bat and any other species wishing to use it. The culvert had the additional enhancement of a bat ‘hot-box’ within the culvert (bat boxes on the roof of the culvert) and had extensive hedging and planting both to the north and south of the road to guide species into its openings. Within a section of hedgerow at the eastern end of the scheme was a reptile hibernacula specifically designed to replicate the one lost as a result of the scheme.

Working with English Heritage

A Scheduled Monument and two Grade II Listed Milestones lie alongside the route. The alignment was carefully designed around the Scheduled Monument, Peverell’s Cross, and its surrounding area to ensure the designation is adequately protected from the road.

Enhancements such as the provision of an information board were agreed with English Heritage to provide historic information about the Cross and surrounding area. Guidelines have also been produced on the restoration of surrounding historic guideposts which targets certain granite posts requiring repair and a spruce up.

As well as the improvement to the road resulting in reduced congestion, driver frustrations and the detrimental impact on the local economy, a Sustainable Drainage System now caters for the increased hard surface being introduced, manages rainwater run-off and provides opportunities for improving water quality and biodiversity. This was a vast improvement to the previous situation where water left the carriageway and drained into adjacent land and water courses.

Ecological input during the design of the three attenuation basins had resulted in lots of enhancement opportunities such as ‘soggy bottoms’ (grassed bottomed basins which remain soggy), basins of varying depths to cater for different species requirements and gently shelved sides to allow species to escape. The design of these has also brought landscape benefits as the basins are less-engineered and are more in-keeping with their surroundings.