Background

Since the 1970s more and more traffic has been using SH2, which has resulted in congestion and safety issues. Strategic studies by the NZTA (formerly NZTA) indicated the section of SH2 between Melling and Petone needs upgrading to address the growing delays and accidents that happen on this section of the highway. Also, the existing access points between SH2 and Hutt City did not work as well as they could, meaning road users experienced delays and congestion because of dated layouts and insufficient capacity at the existing intersections with SH2.

The current connections are at Melling, Dowse Drive, Korokoro and Petone. Of these four connections, there were three sets of traffic signals between Dowse Drive and Petone that did not perform well and did not distribute traffic onto local roads and SH2 well. This led to delays at intersections, delays at local roads and continuing accidents at intersections. Considering the future, research showed that if nothing was done to improve the road, traffic would eventually try to avoid the delays on the state highway by using local roads as a bypass. This would result in congestion elsewhere and an increased risk of accidents on local roads. For the benefit of all road users, this could not be allowed to happen.

A strategy and option analysis has shown that the best improvement for the section of SH2 between Melling and Petone is with raised interchanges, technically referred to as grade separated interchanges, completed in stages. The first stage, immediate works, was the Dowse to Petone Upgrade (D2P) project. Included in this project was the construction of a full interchange at Dowse Drive akin to the Mungavin Interchange in Porirua where a roundabout sits above the highway and connects with a series of on and off ramps. The D2P project was to provide full connection between SH2 and local roads, an overbridge at Korokoro (similar to the Normandale overbridge) and safety improvements between Korokoro and Petone.

Changes at these points have been successful by reducing the growing delays at intersections, separating local and regional traffic, reducing accidents by removing intersections, reducing the potential for accidents along the highway with a better design, and redistributing the traffic flows so motorists making short local trips remain on the local roads while motorists on longer trips use the state highway.

The project also meets Hutt City objectives, including: direct access from the Western Hill suburbs to the network while still providing access to the State Highway, improved and safer access to the Korokoro Industrial Area (KIA), a southern "gateway" access to the Lower Hutt CBD and some relief to existing traffic problems on Petone Esplanade and the southwestern area of the city's roads, which assists businesses and industries that use these routes.

The second stage involves the construction of another raised interchange at Melling. An investigation into improvements between Melling and Haywards Interchange commenced in 2009.

NZTA undertook a joint study of the the state highway triangle of Tawa to Ngauranga, Ngauranga to Petone and Grenada to Gracefield link with Wellington City Council and Hutt City Council. Its recommendations included further investigation of a new road linking Grenada on SH1 with the Hutt Valley.

Overall the Dowse to Petone Upgrade project provides safety, efficiency, access and a level of service expected of a state highway. It provides an "expressway" style facility with enough capacity to move off-peak traffic without too much delay, provides a safer state highway where through and local traffic functions don't conflict with each other and reduces travel time.