At long last the A303 Scientific Committee website has gone public.
A303 Scientific Committee http://a303scientificcommittee.org.uk/
The Scientific Committee has been set up in 2017 at the request of Highways England in the context of their A303 Stonehenge: Amesbury to Berwick Down Road Scheme where it relates to the World Heritage Site (WHS) and its Outstanding Universal Value (OUV), to provide advice in relation to historic environment impacts as the project proceeds through its design, assessment, mitigation and construction stages.
Its membership comprises recognised, leading, independent experts on specific aspects of the landscape of the Stonehenge WHS who can provide additional advice and make a positive contribution to the development of the project. They are all subject matter or period specialists with a specific skill set or depth of experience in aspects of the historic environment of the WHS. The Committee is chaired by Sir Barry Cunliffe and works to an agreed Terms of Reference which will enable it to fulfil the role.
The Committee has the task of advising and guiding the development and delivery of the project in a way that ensures the historic environment dimensions of the project are clearly and consistently assessed and managed for the protection of the OUV of the WHS, and of the historic environment in general within the WHS. It will also ensure excellence in the design and provision of archaeological assessment, evaluation, mitigation and fieldwork.
This web site has been set up in order to share the work that the Committee is undertaking and to make archaeological reports and other documents available to the public.
Reports and minutes are starting to be put up on its pages; one to keep an eye on.
I.E. Scientific Committee Minutes 05 October 2017
• The committee asked whether the western portal could be located outside of the WHS. Highways England explained that due to topographical constraints (the portal needs to exit in a hill face); the nearest alternative portal location would be over 500m to the west of the existing Longbarrow roundabout.
• This would add another 2km to the length of the tunnel and add over £600m to the cost of the scheme. This would make the scheme unaffordable and would reduce the value for money assessment (Benefits to Cost Ratio) of the scheme below the threshold required for it to progress.
• The committee expressed the view that the benefits to the WHS of a longer tunnel would outweigh the additional construction costs due to the unique setting of the WHS. It was a once in a lifetime opportunity that warranted the additional expenditure and that the opportunity should exist to present this argument to the government.
• In discussion it was noted that by promoting a tunnel solution, the government is already committing to spend over £1bn on heritage improvements to the WHS above the do minimum solution of an at-grade dual carriageway through the WHS.
• A discussion was had regarding the setting of the barrows in the vicinity of the A360 junction. It was agreed that diverting the A360 to the west of the existing junction will improve the setting of these barrows.
• Highways England introduced the concept of green bridges to provide connectivity across the new A303. The committee recommended that a suitable location for one of these bridges would be at the Longbarrow Junction along the line of the existing A360.
• The committee asked whether the width of the bridges and their frequency could be extended to provide more coverage of the new A303 through the WHS.
• Highways England explained that there are limits on the width of the bridge before it is considered a tunnel. At the meeting this length was given as 200m, subject to further confirmation. Post Meeting Note –“A road tunnel is a subsurface highway structure enclosed for a length of 150m, or more” - ref: DMRB, Vol 2, Section 2, Part 9, BD78/99, clause 1.2.
• A discussion took place on whether the road through the WHS at the western end should be in cut to hide the traffic from critical views or at existing ground level, and whether if in cut the cut slopes should be formed of soft green slopes or engineered vertical walls.
• Having the new road at existing ground level would allow part of the existing A303 to be used as the eastbound carriageway in the final road layout. This would minimise the amount of new construction within the WHS.
• The committee was of the view that having traffic visible would not outweigh the benefit of re-use of the existing carriageway and would have a greater adverse impact on the OUV.
• Having the road raised above existing ground level such that the existing archaeology is protected below the new road construction was also not considered a suitable option for similar reasons.
• Minimising the footprint of the road within the WHS was a key requirement.
• The committee therefore ruled out the use of soft cut slopes through the WHS as these would more than double the width of the cut, and advised that the cut should be formed with vertical walls.
• To soften the visual impact at the top of the walls, a short height of soft slope would be desirable.
• Highways England will present the visual impact of the scheme in cut through the WHS with the incorporation of green bridges where the bridges provide beneficial mitigation to any adverse impacts and seek the committee’s further views at a future meeting.