Cutting across the iconic, 4,500-acre Stonehenge and Avebury World Heritage Site, the A303 single carriageway sits just 165 metres from the iconic stone formation. Highways England were looking for an innovative, value-led solution for a new route to relieve congestion and minimise impacts to the historic site. Using environmental and geotechnical engineering, the heritage site’s new route involves upgrading to a high-quality dual carriageway, including a proposed 2.9km tunnel as a pioneering central feature.

Arup formed a joint venture with Atkins to help Highways England select the scheme’s preferred route, in collaboration with local communities, and important national and international stakeholders. 

The venture team conducted in-depth investigations and evaluations to understand the impact on this treasured historic landmark, whilst simultaneously recognising the impacts on the cultural environment by liaising with the National Trust and ICOMOS/UNESCO. These conversations led to the final choice of route being positioned in the western half of the heritage site.

The programme was successfully accelerated by the team - swiftly delivering options in just 20 months and saving an incredible one year on the standard duration of a Highways England options phase study. This immense achievement translated into savings in the region of £5m on the contract costs and £50m of forecast construction cost. We aimed to approach the project in a sensitive and understanding manner that respected the significant location, carrying out structural design services, including the tunnel design - in addition to urban economic planning and consulting with relevant people and organisations. 

Urban economic planning 

The heart of the Arup’s economic analysis were the societal impact assessments. Working alongside Simetrica, a specialist team of consultants and academics that specialise in this field, we applied contingent valuation (CV) to assess monetary values for non-market goods. This was completed by asking the public about their willingness to pay (WTP) or willingness to accept (WTA) compensation for a particular change to the urban economy. 

By validating this advanced method, the team obtained a combined net benefit of the scheme of £1.5bn compared with just £500,000 if cultural heritage impacts were not considered. This successfully enabled the team to highlight that the scheme offered value for money. 

A before and after visualisation of the A303 Stonehenge road upgrade
A visualisation of the tunnel solution before and after the road upgrade © Highways England
A303 Stonehenge map of modified alignment
The modified alignment (Sept 2017) also avoided any risk of the road intruding on the view of the setting sun from Stonehenge during the winter solstice, perhaps the most important sightline in the entire World Heritage Site. Image © Highways England

Stakeholder engagement

Since the heritage site is of great significance, it was important that the planning team tackled the task with secured support from a diverse set of stakeholders and advisors with a fleet-footed Stakeholder Engagement and Communications Strategy (SECS). Designing the tunnel alignment resulted in regular meetings with the client, construction advisors, Tunnel Design Authority, and key stakeholders.

The stakeholders included the National Trust, English Heritage, Historic England, Wiltshire Council and Wiltshire Fire Services. A staggering 10,000 individuals and organisations responded to the consultation, using an intelligently applied narrative. This narrative was based on the analysis from the stakeholders, utilising innovative social media posts, stakeholder ‘in their own words’ videos, sound lab projections, and before-and-after imagery and displays.

Tunnel Design

Arup and Atkins’ joint venture team played a huge role in designing the central feature of the proposal – the 2.9km tunnel. Our designs were produced through a rigorous ground investigation, archaeological field evaluations and drone surveys. 

The conceptual design considered major factors, such as tunnel safety and environmental constraints. Using our Tunnel Optimisation Tool (ToT), thousands of alignment options were filtered to select the optimum choice. The tunnel will be constructed with sprayed concrete linings or using earth pressure balance tunnel boring machines, with both options considering the unusual geological phosphatic chalk conditions on site.

I cannot fail to be impressed by how well the team has collaborated in an exemplary manner to deliver all that has been asked of it....and more!

Derek Parody

Highways England, A303 Stonehenge Project Director