The A303 upgrade between Amesbury and Berwick Down includes the 1.8 mile-long tunnel, eight miles of new dual carriageway and a bypass north of Winterbourne Stoke.
The so-called southwest expressway will link the M3 in the southeast and the M5 in the southwest to speed journey times.
A tunnel near Stonehenge is expected to remove (or at least reduce) traffic jams near the famous landmark. It will also reconnect the two halves of the 6,500 acre World Heritage site, which is currently split by the road, and remove the sight and sound of traffic from the Stonehenge landscape.
Following public consultation, Highways England has modified the plans, including moving the position of the western tunnel portal to avoid conflicting with the solstice alignment. The western part of the tunnel is now closer to the existing A303 alignment than it was before the consultation. Highways England said that tweaks to the route ensures that "the Stonehenge World Heritage site will be protected and enhanced for people from across the world to enjoy".
Government policy is to upgrade all remaining sections of the A303 between the M3 and M5 to dual carriageway standard, starting with three schemes: one at Stonehenge, one between Sparkford and Ilchester and the third on the A358 between Taunton and Southfields.