The 12km SH18 Upper Harbour motorway (Upper Harbour Corridor) is a toll road that links North Shore City and Waitakere City. The motorway integrates road transport in the area by forming the northern section of the north-south running 48km Western Ring Route.

Upon completion, the Western Ring Route will provide an alternative to the SH1 route between Manukau City in the south and Albany in the north via the SH20, SH16 and the new SH18.

The SH18 has been constructed in three sections, these include the Upper Harbour Bridge duplication, which opened in 2006, the Greenhithe Deviation, which opened in December 2007, and the Hobsonville Deviation, which opened in August 2011. The project was managed by the New Zealand Transport Agency.

Hobsonville deviation

"The project cost NZD$35m and involved 85,000m³ of earthwork, 900t of asphalt, 8,350m³ of concrete."

The NZD$220m Hobsonville deviation is the final project for the SH18 motorway and is a 6km section of four-lane highway between Albany and Westgate. This project includes a 3km four-lane extension of the SH16 at Brigham lane to integrate the connection between the SH18 and SH16 motorways.

The project involves four interchanges at Hobsonville Road, Brigham Creek Road, Trig Road and Buckley Avenue and a new interchange with the SH16 at Brigham Creek, for north and south-bound SH16 traffic.

The work on the Hobsonville deviation began in September 2008. It was carried out by HEB Smithbridge Construction along with Opus International Consultants and Maunsell Ltd. Bartley consultants and Aurecon were part of HEB lead design and build consortium.

Construction was completed by August 2011, six months ahead of schedule. Work to relocate a Watercare pump station and create a stormwater pond near Westgate shopping centre as preparation for the project were completed in 2007.

Structures and works for the project include: a single flyover at Westgate to the connect SH16 to the new SH18, five bridges situated at Hobsonville Road, Trig Road, Brigham Creek Road, Buckley Avenue and Totara Creek, one cable-stay pedestrian footbridge at Clarks Lane, four new roundabouts along Brigham Creek Road and Sinton Road extended to a new roundabout with Brigham Creek Road.

Extensive earthworks were required to convert the hilly area into a motorway. The construction involved around 1.4 million m³ of earthworks, 350,000m2 of pavement works and 196,000t of asphalt. Around 35,000 vehicles pass through the motorway each day.

Upper harbour bridge duplication

The duplication project for the Upper Harbour Bridge, which was completed in December 2006, involved the construction of a new 458m cantilevered bridge by the side of the existing bridge to connect Greenhithe (east) to Hobsonville (west).

The two bridges provide three lanes towards Greenhithe, two lanes towards Hobsonville and a separate 3m-wide shared pedestrian and cycle path. The project also involved the widening of an 860m stretch of the approach road to the bridge from Hobsonville.

The project cost NZD$35m and involved 85,000m³ of earthwork, 900t of asphalt, 8,350m³ of concrete. The contractors for the project were Fletcher Construction Company as the general contractor and Beca as the engineering consultancy.

Greenhithe deviation

The Greenhithe deviation is a 5.5km length of four-lane barrier segregated motorway running between Paul Matthews Drive (east) to the start of the Upper Harbour Bridge (west).

"The 12km SH18 Upper Harbour motorway (Upper Harbour Corridor) is a toll road that links North Shore City and Waitakere City."

The project, which cost NZD$110m, involved three grade separated interchanges and bridges at Albany Highway, Tauhinu Road and Greenhithe Road.

The Albany Highway interchange has a 37m bridge with two spans and six lanes crossing the motorway. The interchange gives access to eastbound traffic joining the Northern Motorway (SH1), and westbound traffic travelling to Waitakere from the North Shore area.

The Greenhithe Road interchange has a 42m bridge with two spans carrying Greenhithe Road over the motorway. The Tauhinu Road interchange features a 47m-long curved bridge with two spans to carry Tauhinu Road over the motorway (this is the end of the motorway until the Hobson Deviation project is complete).

The project has involved 1.2 million square metres of earthworks, 58,000m³ of pavement, 7,500t of asphalt, 120 piles totalling 1.8km in length and 5,00 m³ of concrete.

The contractors for this project included Opus International Consultants, Maunsell Ltd, Downer EDIWorks and Works Infrastructure Ltd. The project was completed in November 2007 and opened in December 2007.