Work to build the 13km expressway from Peka Peka to Otaki in the Kapiti Coast is set to begin mid-next year.
The new four-lane road will run along the existing State Highway One route, and adds to the Mackays to Peka Peka motorway and Transmission Gully.
The Transport Agency (NZTA) has awarded the project to Fletcher Construction.
The road is expected to cost $330 million, up from $250m, and to open in 2020.
NZTA said Fletcher would work on a detailed design for the project, and there would be further community consultation.