15 miles of the M27 will have an extra lane created in both directions, with upgraded signs, signals and technology to inform drivers about conditions ahead.
On Tuesday, plans about the upgrade have gone on show ahead of the start of main construction.
Highways England delivery director Mike Grant said: "This upgrade of the M27 between Southampton and Fareham will tackle congestion and improve journey times not only for the tens of thousands of drivers who use the M27 every day, but also holiday makers using this busy stretch of motorway to get to the south coast ports as well as the South West of England."
"Smart motorways are central to our ambitious plans for modernizing the motorway network and will add 120 miles of new lanes to motorways in the South East by 2020. They add vital extra capacity, improve journey times and maintain high levels of safety. Drivers will also see better information about conditions through new smart motorway technology which helps us to manage incidents, smooth traffic flow and make journeys more reliable. I encourage anyone interested in this upgrade of the M27 to a smart motorway to come to meet the project team at one of the information events, starting this Friday, June 22 in Southampton."
Drivers, business owners and local residents are invited to find out more about the plans, which will add an extra lane in each direction to the M27 from junction 4 near Southampton (the interchange with the M3) and junction 11 for Fareham, to upgrade it to an all-lane-running smart motorway. New technology will help to manage traffic to reduce delays and give drivers up to date information about conditions on the road ahead.
The M27 is a key strategic road which runs between Cadnam, to the west of Southampton, and Portsmouth and connects the M27 with the M3, and major routes into London and the rest of the UK. Around 140,000 vehicles use the M27 each day.
This stretch of the M27 is heavily used by traffic travelling along the south coast and suffers with heavy congestion, especially during UK holiday periods. The upgrade to a smart motorway will add a third extra capacity on this section, and will improve safety, ease congestion make journey times more reliable.
Under the plans, the hard shoulder will be permanently converted into a live running lane between junctions 4 and 11 in both directions. New signs and signals will be used to vary the speed limit to reduce congestion at busy times, and to control traffic if there is an obstruction on the road ahead.
Preliminary work is already underway, with main construction scheduled to start later this year. The smart motorway will be fully operational in 2021.