Work is under way on repairs and reinstatement of the damaged section of the retaining wall at Anzac Parade next to the City Bridge.
New Zealand Transport Agency (NZTA) regional transport systems manager Ross I'Anson said the project would return the state highway to its full and unrestricted lane width, including reinstating the cycleway and footpath.
The cycleway and footpath was closed after the June 2015 flooding when the underslip resulted in "significant loss to the road shoulder" which is now being repaired.
"These works have taken some time to commission as the site is very complex and we have had to undertake extensive investigation and design works," said Mr I'Anson.
"We're pleased the repair work is now able to get under way."