Wellington's Transmission Gully motorway "is scheduled to open before Christmas 2020," the NZ Transport Agency said.
The ageny has also provided significant additional financial relief to the motorway's makers because of a number of issues experienced during the construction.
NZ Transport Agency interim CEO Mark Ratcliffe said the financial settlement with the joint venture builder CPB HEB JV will ensure the gully route "is completed to a high standard, meets the needs of customers and still achieves good value for money for New Zealanders.
"Transmission Gully is a highly complex project being built on 27km of very difficult terrain.
"Progress has been slower than anticipated due to a number of issues encountered during construction including the Kaikoura earthquake in 2016 which diverted resources and materials.
"Construction has been impacted by the challenging conditions of the site.
"The project has required an increased earthworks programme, creating further complexity, disruption and cost to the project through the additional consent requirements.
"These issues, and the impact from several storm events and the Kaikoura Earthquake, have meant CPB HEB JV has incurred significant additional costs to construct the project.
"In acknowledgement that these issues were out of the control of CPB HEB JV and not something they could have reasonably anticipated the Transport Agency has provided $190.6m of financial relief to CPB HEB JV."
He said, "The majority of the money will go towards supporting CPB HEB JV, local sub-contractors and employment while also ensuring the Transport Agency still achieves good value for money for Transmission Gully."
The settlement is conditional on the PPP contractor, Wellington Gateway Partnership, becoming a party to the settlement, he said.
"The parties are working through satisfying the conditions and obtaining the necessary approvals."
"As part of the settlement, CPB HEB JV's historic claims against WGP and the Transport Agency have been resolved without resorting to court action which would have resulted in further costs and delays to the project.
"As with all projects' timeframes and expected completion dates, we are always dependent on good weather.
"CPB HEB JV will be working very hard to complete the motorway by Christmas, subject to good progress through the next six to nine months and to passing a series of standard quality safety and environmental checks prior to opening."
Mr Ratcliffe said once open, there will be further work required before the project is fully completed, including landscaping and testing and commissioning of new technology systems.
"These works will most likely be completed by mid-2021.
"The Transport Agency, WGP and CPB HEB JV are committed to working together to complete the project and we remain excited about the opening of Transmission Gully and the many benefits that it will bring for our customers, Wellington and the central and lower North Island."
The money for the settlement has come from the National Land Transport Fund and will not impact any other projects currently being progressed on the State Highway network.
It is not related to the Government's $6.8b NZ Upgrade Package that was announced in January.
Transmission Gully key facts
* Transmission Gully is a four-lane, 27km motorway running from Mackays Crossing at Paekākāriki to Linden.
* Four interchanges and two link roads will connect the motorway to Mackays Crossing, SH58, eastern Porirua and Kenepuru.
* It includes over 10.2 million cubic metres of earth moved, and cuts of up to 70 metres.
* There will be 25 structures (bridges and major culverts) equating to a total length of more than one kilometre; the largest structure is the bridge over Cannons Creek — 230 metres long and 60 metres high.
* More than 534 hectares of ecological mitigation areas and 27km of stream remediation, restoring native landscapes and mitigating the sedimentation effects of the project on waterways.