World heritage body Unesco has expressed concern over the impact plans for the 2.9km long Stonehenge tunnel would have on the site.
The body said the new tunnel and associated 2.2km of dual carriageway approach roads could ‘adversely’ affect the Outstanding Universal Value (OUV) of the property.
In a report submitted in late March and made public this week, the World Heritage Committee responded to plans put forward by Highways England which is proposing to upgrade the existing single carriage A303 road running through the site.
At present the road runs within 165m of the monument and increasing volumes of traffic, especially in the summer months, causes long delays and congestion.
The scheme put forward by Highways England proposes to bypass the stones and increase capacity by dualling the single carriageway and creating an ”invisible” road by tunnelling away from the monument.
However the report stated the current proposal had not ‘afforded sufficient priority to the OUV of the property’ and was is now urging the authorities to explore further options. This includes an already ruled out ‘F10’ non-tunnel by-pass option to the south and a longer tunnel option to move the portals and cuttings.
“Considering the iconic status of the property, the State Party [secretary of state for transport] and its agencies should continue to proceed thoroughly and cautiously, to ensure that the optimal solution is identified and implemented for the widening of the A303,” the report said.
“While a range of issues and factors must be balanced, the appropriate approach is to avoid adverse impacts on the OUV of the property. It is not considered satisfactory to suggest that the benefits from a 2.9km tunnel to the centre of the property can offset significant damage from lengths of four lane approach roads in cuttings elsewhere in the property.”
A consultation on the final alignment for the route through the site was carried out in February this year and a preferred route for the road is expected to be announced this summer. However it is expected that both proposed routes will involve the tunnel portals being sited within the WHS.
The Department for Transport (DfT) said not only would a new, non-tunnelled option have a significant adverse environmental impact on the surrounding communities, it would offer a less direct route for through traffic reducing transport and economic benefits. Routes in corridor “F”, it said would also interact less well with local roads and increase ‘rat-running’ through local villages.
A government spokesperson said: “We are investing up to £1.8bn to improve the A303 near Stonehenge so that people can visit the 10,000 acre World Heritage site without the disruption of a nearby major road. We worked closely with Historic England, the National Trust and English Heritage to develop these plans and they have welcomed the significant benefits our proposals will bring to the protection of Stonehenge.
“Upgrading the road will cut congestion, improve journey times and provide a huge boost to the economy in the South West as it links people with jobs and businesses with customers.”
The transport secretary will have the final say on the design which is expected to be finished by late 2019 with construction anticipated to start in March 2020.