Construction of a new dual two-lane road to replace the existing single two-lane A358 between Taunton and Ilminster. The new road is likely to be built to Highways England's new "expressway" standard and may incorporate parts of the existing road in places.
It is not yet clear whether the scheme will incorporate an improved junction with the M5, or whether it will lead directly onto the A303 Ilminster Bypass rather than taking a less direct line to terminate at the Southfields Roundabout as at present.
This scheme is one of a number of improvements to the A303/A358 route between the M3 and the M5, and once completed will form the western end of the A303 route. It is intended that through traffic for Devon and Cornwall will then use the A358 from Ilminster to the M5, and not the existing A303 and A30 through the Blackdown Hills towards Honiton. It is not known whether this section of road will then assume the number A303, but it remains a possibility.
To some extent, this scheme is dependent on the success of the Stonehenge Tunnel (the A303 Amesbury - Berwick Down scheme), without which other improvements to the A303 and A358 will not be considered worthwhile.
This scheme is part of the Expressway to the South West programme of works.
A second consultation on the preferred route by Highways England closed at the end of February 2018. A consultation report will be prepared, and this will be published when they make their preferred route announcement, which is expected in late 2018, according to Highways England.
A preferred route has now been announced. A modified version of the "pink route" is being taken forward for further development. Proposals for a free-flowing link between the A358 and the M5 to the south, bypassing junction 25, have been dropped. Southfields Roundabout will also remain intact, and bypassing or grade-separating it will form part of a future scheme to dual the A303 Ilminster Bypass.