UK-based Highways England has unveiled an initial plan to build a tunnel as part of the £1.6bn upgrade of the A303, which passes through Stonehenge.

The new proposal is open for a public consultation period that will run until 6 April this year.

The construction of the nearly two-mile tunnel is expected to reduce traffic congestion on the A303, however, various heritage and archaeological groups have expressed their concern that it may damage the Stonehenge monuments.

The latest design, revised from the earlier announced preferred route, claims that the tunnel will not cause any damage to the Wiltshire archaeological area and will make it easier to reach and explore the sites.

“We are very concerned about the detrimental impact of traffic on the byways and believe this will be made worse by the proposal to link existing byways after the surface A303 is removed.”

Heritage groups such as English Heritage, Historic England and the National Trust have welcomed the new design, reported media sources. However, these groups have also expressed their concerns about the proposals to connect two ancient byways, currently separated by the A303.

The three groups were quoted by The Guardian as saying: “We are very concerned about the detrimental impact of traffic on the byways and believe this will be made worse by the proposal to link existing byways after the surface A303 is removed.”

Within the consultation period, a series of public events will be conducted.

The authority noted that the feedback from the consultation period will help to develop the scheme further before the application submission by the end of this year for consent from the Planning Directorate.

Construction of the project is expected to commence from 2021.