Project introduction

The State Highway 20 Mt Roskill Extension extends the Southwestern Motorway 4.5km from Queenstown Road in Hillsborough through Mt Roskill to Maioro Street in New Windsor. The motorway has two interchanges and incorporates provision for future bus shoulder lanes and rail.

  • Estimated project dates

    Sep 2005–May 2009
  • Estimated project cost

    $100 million +
  • Project type

    Road improvements
  • Project status



The purpose of the State Highway 20 Mt Roskill Extension is to create a further key link in the Western Ring Route, providing a high standard, strategic extension of the highway from Queenstown Road through to Maioro Street.


  • Creates a key link in the Western Ring Route that when completed, will help to ease congestion on State Highway 1.
  • Improves traffic flow on local roads by separating motorway traffic and local traffic with new overbridges.
  • In the future will provide a key link to Auckland International Airport from the Auckland central business district.

About the project

This project was completed on 15 May 2009.

SH20 Mount Roskill Extension is a key part of the Western Ring Route. Once completed, the Western Ring Route will provide a genuine alternative to SH1 between Manukau City and Albany via SH20, SH16 and SH18.

The $186M State Highway 20 Mt Roskill Extension was completed on 15 May 2009. This four-lane, four kilometre motorway extension provides an alternative regional route through greater Auckland, linking the cities of Manukau, Auckland, Waitakere and North Shore.

The extension itself also provides considerable relief to local roads in the Mt Roskill and Avondale areas that previously carried through traffic from the Southwestern Motorway (SH20) to the CBD and Auckland’s western suburbs.

Project timeline

  • Contract signed July 2005.
  • Construction start 30 August 2005.
  • Construction completion 15 May 2009.

Concrete rock

A ‘shotcrete’ method was used on the piers of the Dominion Road Bridge to create an artificial exposed surface showing the dark red colour and form of the original basalt rock found during construction. The surface was sprayed with concrete and then shaped by hand using templates from the existing rock surface, to create a natural looking face. This surface provides a visual reference to the natural volcanic characteristics of Mt Roskill, which is located directly behind the bridge.