The work would raise and widen a 3.3km section of Portobello Rd from Luss Rd, Company Bay, to Sandpiper St, Broad Bay, the Dunedin City Council said in a statement.
Traffic would be reduced to one lane during construction and manual traffic control would be in place to manage queues.
Access to side roads and resident driveways would be maintained.
The work is scheduled to take 18 months, and is expected to be completed in July 2021.
Council transport delivery manager Josh von Pein said council staff were "working hard to co-ordinate the work to minimise the disruptions as much as possible".
"We’re grateful to the public for their co-operation while this work is being done."
The Vauxhall-Macandrew Bay section of the Peninsula Connection was still under construction and was due to be completed in June next year.
So far, 2.2km of the 4.4km section of road-widening has been sealed and a new seawall has been completed along the full length.
The section from Bacon St to Portobello was completed in May this year, although minor work to raise pump stations was ongoing.
The section from Broad Bay to Turnbulls Bay is scheduled to begin in mid-2020.
