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Improving the A303 between Amesbury and Berwick Down


On the 20th of May the NAO (National Audit Office) published a report on risks and uncertainties surrounding the UK government’s plan to build the tunnel project beneath the Stonehenge world heritage site. The project forms part of the A303 and A358 road corridor which links the South East and South West of England. The Department for Transport aims to upgrade the entire A303/A358 to dual carriageway before 2029 through eight individual projects. The Amesbury and Berwick Down project involves building a tunnel 3.3km long beneath the Stonehenge World Heritage Site.

The Department and Highways England expect the tunnel to reduce congestion, support economic growth and improve the setting of the World Heritage Site. It is forecast to cost between GBP1.5 billion and GBP2.4 billion, subject to funding approval from HM Treasury and the outcome of commercial negotiations with contractors, with a likely cost of around GBP1.9 billion (including VAT).

The NAO report says the project is only estimated to deliver GBP1.15 in benefits for every GBP1 spent, in part due to the high cost of building a tunnel.

Highways England believes there are significant additional benefits if all eight projects, covering the entire road corridor, are completed and that this will maximise its return on investment on the Amesbury to Berwick Down project.

The Department intends to approve each project on its own business case and has committed to start two other projects alongside the Amesbury to Berwick Down project by March 2020. However, it considers the remaining five projects to be low to poor value for money.Highways England may therefore struggle to justify future investment if they are assessed on an individual basis. If it does not upgrade the whole corridor, it will not be able to help unlock the full growth potential in the South West.

The Amesbury to Berwick Down project has been delayed because of decisions about how it will be funded. By February 2019, Highways England had spent  GBP53 million on the project. HM Treasury has granted it a further GBP21.5 million of funding for pre-construction works.

There are risks that both the Highways England and the Department will need to manage to ensure the project has a realistic chance of delivering value to taxpayers. Highways England is still working to an open date of December 2026 despite delays to the project, resulting in a very tight construction timetable. There are also geological and archaeological risks. While Highways England is working to lessen these risks, it also needs to make sure it can support the project throughout its life; the operation, maintenance and renewal costs are expected to be GBP524 million (2016 prices) over 60 years.

Previous attempts to construct a tunnel have been cancelled due to escalating costs and disagreements between stakeholders. Highways England has managed to gain agreement in principle from key stakeholders such as the National Trust and Historic England but other bodies, including the UNESCO World Heritage Committee, have raised concerns.

The NAO recommends that Highways England and the Department keep in view the open to traffic date of December 2026 to ensure it remains realistic. They should also engage effectively with other government departments and stakeholders to ensure all the expected benefits of the project are delivered.

Click here for the full report, here and uk/34 for tunnelbuilder archive. Also visit