Stonehenge tunnel: Salisbury bypass considered as alternative
A southern bypass of Salisbury is being considered as an alternative to a Stonehenge tunnel, the BBC has learned.
The government announced in 2014 that it wanted to build a tunnel alongside the World Heritage site.
But Highways England is also considering a route which would take the A303 south of the city.
A £2bn 1.8-mile (2.9km) tunnel is the government's preferred option at Stonehenge but some archaeologists argue it could damage the ancient site.
In an email, seen by the BBC, Highways England suggests a southern bypass route would be "considered" as part of the "design consultation" phase of the upgrade.
Last week, Atkins/Arup was awarded a £17.5m design contract for the scheme.
The group will be "developing options" to upgrade the road - including that of a tunnel - with the aim of construction work starting in 2020.
Congestion on the A303
Proposed cost of Stonehenge tunnel
1.8 miles is the length of the proposed tunnel (2.9km)
9.6 sq m around Stonehenge is a World Heritage site (25 sq km)
33% of the route is single carriageway
84 years since the A-road opened
There are growing concerns over congestion on the A303 which has been described as "highly detrimental" by English Heritage, which manages the monument.
However, a group of historians - called the Stonehenge Alliance - has called for "no further damage" to the world heritage site.
Historian Tom Holland, from the group, said the southern option was "better than ploughing through the richest archaeological site in Europe" and called for "lateral thinking" over A303 congestion.
And Icomos, which advises UN cultural body Unesco, said it was "concerned" any upgrade could have a "highly adverse impact" on the World Heritage landscape around the stones.
Both English Heritage and the National Trust have given their support to the option of "the longest tunnel possible".
In a statement, Highways England said: "As part of our public engagement we are committed to considering the alternative routes that are being suggested and will look at these as part of our engagement work.
"The improvements are currently at an early stage of development. As we develop our proposals in compliance with the statutory processes, we will consult a variety of stakeholders, including local residents, businesses, road users and interested parties.
"We are aiming to start a wider and public consultation in early 2017."
A similar tunnel scheme for the route, which links London and the South West, was dropped in 2007 because of the spiralling cost.
The government said the cost of a bored 1.3m (2.1km) tunnel could not be justified at £540m - double the initial estimate of £223m.