A £2.7m scheme to improve traffic flow on the congested A350 north of Chippenham starts at the end of this month.
Wiltshire Council hopes to rid the route of its significant peak time delays and pump £5.9 million into the local economy by creating jobs.
Drivers are being told to expect improved journey times when work is finished in early 2015, slightly later than the original planned finish date of December.
In the meantime disruption is said to be inevitable, but the council hopes the use of traffic lights will keep it to a minimum.
The road will be kept open to two-way traffic throughout the day, by putting a 30mph limit in place during construction to ensure the safety of site staff. There will be a series of overnight closures to allow specific items of work to be carried out safely.
At the moment dual carriageway runs from the M4 junction 17 for about 2.5 miles up to the Jacksom’s Lane junction.
The work will extend it by another 600 metres in both directions, taking it to the Badger roundabout next to Morrisons.
It will also improve the pinch point Malmesbury Road roundabout and add a signal controlled crossing nearby.
John Thomson, cabinet member for highways, said: “This is a very important route, one which has typically been a bottleneck.
"Although there will be some disruption while the work is ongoing, the outcome will help improve journey times and ease the congestion around this area.
“Wiltshire is already very well connected in terms of transport links and this investment will bring economic benefits to the county as Wiltshire becomes an even more appealing place for businesses looking to relocate to.”
It will start with major work by utility companies to divert their services, followed by the main dualling work carried out by the council contractors.
It was announced last May that £1.9m had been secured from the Local Pinch Point Fund (LPPF), a fund designed to support schemes that tackle congestion or address the condition of highway structures that are close to becoming a barrier to access.