If implemented the road would serve as a lasting indictment of our treatment of the surroundings of a place that is known and esteemed throughout the World as the icon of our nation's heritage.
On 1st December the Government announced its intention to dual the single-carriageway stretch of the A303 between Amesbury and Berwick Down, including a 2.9km bored tunnel under the central part of the Stonehenge World Heritage Site (WHS) but south of the henge itself.
The project is one of a number of Department for Transport schemes to improve traffic flow along the A303 / A30 / A358 corridor, aimed at boosting economic and housing development in the South West.
Whether relief of traffic congestion will make much difference is questionable since it is recognized that such benefits are often not realised in practice and road widening in itself usually leads to further congestion within a few years.
A World Heritage Site at risk
The main concern at Stonehenge, however, is the threat posed by the tunnel and its associated road engineering works to the 27sq km of archaeological landscape surrounding the Stones.
The whole area, together with a similar landscape at Avebury, was designated a UNESCO World Heritage Site (WHS) in 1986. Such Sites are recognized to be of 'outstanding universal value': unique and irreplaceable properties that are part of the world heritage of mankind as a whole.
At Stonehenge, the A303 passes right across the WHS, a distance of some 5.4km from Countess Roundabout on the A345 to the east, to Longbarrow Roundabout on the A360 to the west. Of this, almost 2km at the eastern end is already dual carriageway - and that damage is already done.
However to build the 2.9 km tunnel, major earthworks would be involved at both ends, including deep tunnel cuttings, twin portals and huge, grade separated junctions on the eastern and western WHS boundaries.
These works would measure up to 500m in length at either end - and at the eastern end, would need to be accommodated as much as possible within the existing cutting. But at the western end there is no valid reason for them to be within the WHS at all - and that is what a 4.5km tunnel could deliver.
These are major construction projects in their own right that would destroy all archaeological remains in their way. They would permanently scar the landscape with massive, dominating 21st-century features in a landscape specifically designated for its Neolithic and Early Bronze Age remains.
Protective measures disregarded
Under Article 4 of the World Heritage Convention, it is the duty of each State party to "ensure the identification, protection, conservation, presentation and transmission to future generations" of its World Heritage Sites.
Each State is committed to "to do all it can to this end, to the utmost of its own resources and, where appropriate, with any international assistance and cooperation, in particular, financial, artistic, scientific and technical, which it may be able to obtain."
It is impossible to reconcile this explicit undertaking with the road scheme now proposed for a WHS that embraces the world's most famous prehistoric monument.
It's also difficult to understand the support for this planned violation voiced by two of our premier conservation bodies: English Heritage and the National Trust, which both cite the "benefits" the tunnel would bring to the WHS.
True, the National Trust says it would prefer a longer tunnel - but is nevertheless content for our priceless heritage to be surrendered to the bulldozers. A press release quotes Ian Wilson, the NT's Assistant Director of Operations as saying:
"We would like to see the longest possible tunnel but we recognise that any plan needs to be both affordable and deliverable if we're to finally solve this long-running challenge ...
"We're continuing to work with the Government and partner organisations to look at how we best deliver a world class solution for one of the most important pre-historic landscapes in Europe."
UK's advisors to UNESCO: 'impacts cannot be set aside'
But no other heritage or environmental body appears to have stepped forward in support of the project, with Friends of the Earth, the Campaign to Protect Rural England and the Council for British Archaeology (CBA) all expressing strong reservations.
The tunnel "would have major implications for the archaeology", said Mike Heyworth, director of the Council for British Archaeology. "We should be asking whether a major expansion of the roads network at Stonehenge just to meet traffic needs is the most appropriate way to deal with such a site."
And the UK branch of the International Council on Monuments and Sites (ICOMOS-UK), advisers to UNESCO's World Heritage Committee on our WHSs, has informed the Government that the benefit the tunnel could bring to part of the WHS could not be offset against damage to other parts of it:
"Associated portals and dual carriageways could have a highly adverse impact on other parts of the world heritage landscape that cannot be set aside, however great the benefits of a tunnel."
Why is the Natonal Trust so ready to sacrifice our heritage?
So why should the National Trust and English Heritage pre-judge what our Government can afford? No doubt English Heritage, a Government quango, is obliged to look to cost savings.
The National Trust, however, is actively campaigning for a 24.7km bored tunnel for HS2 under the Chilterns Area of Outstanding Natural Beauty, some eight times longer than the Stonehenge tunnel proposal.
Both organisations have failed to condemn destruction of parts of a WHS protected under an international legal agreement. Does the Trust only have its eye on the main chance of restoration of the part of the WHS it owns?
Besides these two heritage bodies, the scheme's supporters in the main are road widening lobbyists. Local Economic Partnerships of the South West want a few minutes knocked off journey times.
Local residents are also fed up with summer and weekend traffic jams, often caused by drivers slowing down for sight and a selfie of the Stones, and with drivers rat-running through nearby villages.
Some say the situation has been deliberately allowed to continue so as to precipitate impetus for road widening. Improvements could, however, be implemented straight away with road design enhancements and traffic management measures to alter drivers' habits - such as road-user charging for non-local traffic at current peak travel times, and devices designed to make rat-running less attractive.
Hydrogeology and ecology
A further dimension to the tunnel project is the unpredictable hydrogeology at Stonehenge. Objectors' specialist evidence on this subject was brought to the 2004 Public Inquiry into an earlier A303 dualling project by the Stonehenge Alliance.
It was shown that engineering the 2.1km bored tunnel then proposed could prove problematic. The scheme was eventually abandoned owing to rising costs resulting from tunneling through
"very large quantities of phosphatic (soft, weak) chalk [and] a high water table, with the ground water potentially rising to the surface at times of heavy rainfall where the tunnel passes below a shallow valley to the south of Stonehenge." (Hansard, Written Ministerial Statement, 20th July 2005: A303 Trunk Road (Stonehenge))
Ground conditions remain unchanged. Furthermore, the River Avon, whose catchment area includes the WHS, is designated a Special Area of Conservation, protected under European Law (Habitats Directive (92/43/EEC)).
The designation here is specifically for Annex I habitats for five aquatic Ranunculus species, and for Desmoulin's whorl snail among Annex II species. Water flow and quality are thus of paramount importance. Any decisions on tunnel length, depth and portals will need to take impacts on hydrogeology and ecology into account.
There will be drainage during construction work and rainwater run-off from completed road surfaces to monitor. Further to these, appropriate measures must be employed to deal with unexpected accidental chemical spills in the vicinity.
What happens next?
It is understood that work is already under way on investigation into what may be feasible in terms of tunnelling at Stonehenge. The Government has agreed to include ICOMOS-UK and the UNESCO World Heritage Committee in its further discussions on the way forward.
Simon Thurley, English Heritage's Chief Executive, said in his press statement of 1st December: "This is about investing in the future. We have a responsibility to future generations to get this right as we provide a world-class solution for a world-class place."
Quite so: and no better case for putting enough money where the mouth is.
Meanwhile the Stonehenge Alliance, a group of national non-governmental organisations, continues to campaign for a tunnel that is at least 4.5km long. Such a tunnel might begin within the eastern cutting for the already dualled section of the A303, and end beyond the western boundary of the WHS.
A 'Save Stonehenge World Heritage Site' petition, launched on 28th October, has already secured over 11,000 signatures and more are urgently sought to change Government's mind.
Clearly, a tunnel of some 6km that avoids the WHS and its setting entirely must be the ultimate goal. Funding should be found and, given the vast sums the Government is proposing to spend on new roads, this should be perfectly feasible.
Anything short of a 4.5km road tunnel would result in permanent damage to archaeology, landscape and setting. The current plan would meet virtually none of the Government's international commitments and, if implemented, serve as a lasting indictment of our treatment of the surroundings of a place that is known and esteemed throughout the World as the icon of our nation's heritage.
It would be infinitely better to leave well alone than to do the wrong thing.
Petition: 'Save Stonehenge World Heritage Site'.
Dr Kate Fielden is an archaeologist and environmental campaigner, and Hon. Secretary to the Stonehenge Alliance. She has been involved in discussions about the management of the Stonehenge and Avebury World Heritage Site for over 20 years, taking part in a number of Public Inquiries into planning and road proposals.
More information: the Stonehenge Alliance is supported by Ancient Sacred Landscape Network; Campaign for Better Transport; Campaign to Protect Rural England; Friends of the Earth; and RESCUE: The British Archaeological Trust.