Transmission Gully Motorway

The Transmission Gully Motorway is a 27 km four-lane motorway proposed for Wellington, New Zealand. Construction officially began on 8 September 2014 and completion is scheduled for 2020.

It will complement the current State Highway 1 along the coast road between the Kapiti Coast, Pukerua Bay and Porirua. From SH1 at MacKays Crossing, north of Paekakariki, the route rises steeply to the Wainui Saddle and follows Transmission Gully down to Porirua Harbour's Pauatahanui Inlet. It continues south around the outer edge of the Porirua urban area, at one point crossing a 300-metre-long and 90-metre-high bridge, and rejoins SH 1 at the boundary of Porirua and Tawa. The length is 27 km, with a maximum gradient of about 8.3%.

Three intermediate interchanges are proposed. The first interchange is with State Highway 58 at Pauatahanui, providing access to the Hutt Valley. The second interchange will link via new local roads to James Cook Drive in Whitby and the Warspite Avenue-Niagara Street intersection in Waitangirua. The third interchange will link via a new local road to Kenepuru Drive south of the Porirua city centre.

Proposals have existed for some time, but it was only late in the first decade of the 21st century that serious steps were taken towards construction. The Greater Wellington Regional Council, in preparing its Western Corridor Plan, initially rejected Transmission Gully as unaffordable, preferring to upgrade the existing coastal route, but changed its position after public consultation.

on 15 December 2009 Minister of Transport Steven Joyce announced the Government's commitment to the project as one of seven Roads of National Significance, with a predicted project cost of NZ$1.025 billion. Construction is expected to start in September 2014 and be "substantially completed" in 2020.

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