Highways England has published two options for fully dualling a congestion-prone section of the A303 in Somerset.
More than 26,000 vehicles per day use the 11km long stretch of road between Sparkford and Ilchester, double the volume it was designed for.
The upgrade will turn the part single, part dual carriageway section into a fully dualled road, completing a 50km dual carriageway between Mere and South Petherton.
Transport secretary Chris Grayling said: “Tackling congestion on this vital road will also help boost the economy in the South West, unlock thousands of jobs and homes and promote tourism.”
The work will also include making junctions safer as well as providing better links for pedestrians and cyclists, said Highways England.
The preferred route will be revealed in the autumn with work expected to start in 2020.
A separate consultation on building a tunnel for the A303 near Stonehenge is also underway.
Why is the upgrade needed?
The A303/A358 corridor connects the South West, London and the South East.
While much of the route is a dual carriageway, there is still over 56km of single carriageway.
These sections are congestion bottlenecks, particularly in the summer and at weekends.
This section of the A303 between Sparkford and Ilchester is a mix of dual and single lane carriageway, subject to localised congestion. This section also has a poor accident record as a result of poor junction alignments and visibility, and changes in road type.