East Cowes on Friday.
The major route takes traffic for the Floating Bridge, Red Funnel's vehicle ferries, big employer GKN, English Heritage's Osborne, Waitrose and more.
Phase four will take in a stretch between Well Road and Adelaide Grove.
When that is complete, resurfacing will start.
Local shopkeepers, reopening under the Covid-19 roadmap, say they are losing business.
As the Covid-19 lockdown eases, half term is likely to bring fuller ferries, from the end of the next week.
Meanwhile, Island Roads says it has made some 'minor adjustments' to the diversion route, which sees artic lorries, HGVs and buses making tight turns on residential roads, and multi-way lights at the junction of Clarence Road and York Avenue.