"Crucial" works to install sets of traffic lights at St Mary's roundabout will commence on August 10.
From that date, construction will also begin on the approach to the B&Q roundabout. Drivers are being warned they will not be able to access the Dodnor estate from St Mary’s roundabout until September 7, at the earliest.
In the meantime, traffic will be diverted via Riverway. Access from the estate to St Mary’s roundabout will be retained throughout the period.
Once access to the Dodnor estate is reopened, works will move to create the Hunnyhill bus link. The Isle of Wight Council says services can operate via Dodnor while Hunnyhill is closed.
The local authority insists construction is progressing well and remains on programme for completion before Christmas.
Plans released today (Tuesday) show the traffic management arrangements for stages of work in place between August 10 and October 12.
During that time, motorists are advised that there may be additional congestion during these phases.
Cllr Ian Ward, Cabinet member for transport and infrastructure, said:
"I am really pleased with the progress which has been made to remain on programme particularly in these challenging circumstances.
“This period will see the most disruptive part of the work although I am pleased it has been planned to minimise that as far as is possible.
"I hope the maps and information we are publishing in advance will help people to plan their essential journeys and we remain grateful for everyone’s continued patience as we progress this important junction improvement.”
The council says, so far, works to the north of the roundabout fronting the hospital have been completed with a new shared footway/cycleway constructed on the opposite side of the road linking to the hospital via a new signal controlled crossing.
The contraflow has also been removed although traffic in each direction remains in a single lane to help manage flows while construction continues on St Mary’s roundabout.
The completion of the new signal controlled junction with Forest Road is nearing completion with eastbound traffic already using the new junction and northbound slip road to Cowes.
An additional lane has been provided around the B&Q roundabout and the dual carriageway northbound approach to St Mary’s roundabout widened in readiness for the new signal controlled junction (traffic lights).
Kevin Burton, Island Roads network manager, said:
“Though the past few months have not been without challenges we are delighted to have been able to maintain progress and keep the project on schedule.
“We are now entering a critical phase which will bring with it some disruption, but after which we really will be on the home straight with the finishing line in sight.
“Part of the reason we have been able to maintain progress is because of the co-operation and understanding residents and businesses have shown.
“I am sure they will continue to work with us as we move through these critical next few phases.”
You can view traffic management arrangements online: https://islandroads.com/