Fulton Hogan and Aurecon have been awarded the contract to replace two of the one-way bridges at Matakohe.
The work represents the first part of the Northland Bridges programme and includes two traffic lanes, as well as a shared path for pedestrians and cyclists.
Improvements also include a realignment of the state highway to remove the tight bends approaching the bridges and a new intersection for the iconic Kauri Museum, and cycling connections along the Twin Coast Discovery route.
Public consultation on the preferred alignment for both the bridges will be held in the first quarter of this year, and construction is expected to start later this year.
The narrow width of the current bridges causes delays during the busy visitor season, and there were 15 reported crashes on or near the bridges between 2005 and 2014.