SH20 Manukau Harbour Crossing

Section menu

Project introduction

Manukau Harbour Crossing doubled the traffic capacity of State Highway 20 between Queenstown Road and Walmsley Road, including duplicating the Mangere Bridge.

  • Estimated project dates

    Feb 2008–Aug 2010
  • Estimated project cost

    $100 million +
  • Project type

    Infrastructure upgrade
  • Project status


Project updates


The Manukau Harbour Crossing project made it safer, quicker and easier to travel on State Highway 20 across Manukau Harbour between Mangere and Onehunga. It has local, regional and national benefits for business, industry and tourism.




  • Improve access to and from south and central Auckland.
  • Increase traffic capacity and provide priority for buses across the Manukau Harbour.
  • Improve travel times to and from the airport.
  • Improve access to local and arterial roads.
  • Provide better links between the Mangere Bridge and Onehunga townships.
  • Provide better pedestrian and cycle links, including access to the Manukau Harbour.
  • Provide future proofing for a rail corridor by shifting the motorway alignment to the east, between the Mangere Bridge and Walmsley Road, and building extra strength into the new bridge’s foundations.

Project features

  • A duplicate motorway bridge over the Manukau Harbour to give four traffic lanes and bus shoulder lanes in each direction.
  • The Southwestern Motorway widened to three traffic lanes and a bus shoulder lane in each direction, extending to Queenstown Road and SH20 Mt Roskill Extension in the north and to Walmsley Road in the south.
  • Replacement pedestrian overbridges at Beachcroft Avenue (Onehunga) and Hastie Avenue (Mangere Bridge).
  • A new pedestrian and cycle overbridge across Onehunga Harbour Road, providing safe traffic-free access between Onehunga Hall and the old Mangere Bridge.
  • A new pedestrian and cycle route under the southern approach of Mangere Bridge from Coronation Road to Mahunga Drive.
  • Protection and enhancement of the natural, social and physical environment around the project area by:
    • managing the project in an environmentally responsible manner
    • protecting and enhancing the local environment
    • implementing systems to reduce construction waste
    • minimising dust and noise
    • extensive landscaping and planting.
  • Enhanced treatment of stormwater from the motorway to improve the quality of water entering the Manukau Harbour.
  • Reinstatement of the Waterfront Road Reserve upon completion of the project.

Our partners on this project