The Dowse Drive to Petone section of SH2 is bounded by severe physical and operational constraints. Along its western edge, the route is located along the scarp of the Wellington Fault (also referred to as the "western escarpment"). To the east, the Wairarapa and Melling Branch railway runs the full length of this section of the highway. The section of SH2 between Korokoro Intersection and the Petone overbridges runs through an industrial area and is referred to in this project as the Korokoro Industrial Area (KIA).
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.
A number of preliminary studies on potential noise, ecological and visual effects were undertaken to assist with the selection of preferred options for the Dowse to Petone Upgrade project.
Further details of the studies undertaken can be viewed in the reports entitled "Report on Environmental Issues" and "Option Evaluation Report" prepared for the consultation process.
An "Assessment of Effects on the Environment" (AEE) was prepared and lodged with the application for the Notice of Requirement and resource consents with local consent authorities in March 2001. The AEE was based on the preliminary reports referred to above.
The AEE highlighted that within the project area for the proposed Korokoro overbridge and Dowse Interchange there were no significant vegetation or aquatic habitats. However the report also stated that the off ramps from SH2 to the new Dowse interchange would affect part of Percy Scenic Reserve, which contains a garden of rare and endangered plants. A mitigation package for the works was prepared in consultation with affected parties.
Results of noise impact analysis for road and construction noise showed that any increase in noise levels were not expected to be significant and overall road traffic noise was unlikely to exceed the NZTA's national guidelines. The area at the western end of Hume Street has had post construction monitoring to confirm compliance.
Visual effects of the project, as expected, are moderate due to the scale of the landscape and largely built up urban area environment. Most of the effects have been addressed through appropriate landscaping.
Approvals under the Resource Management Act
The Notice of Requirement (NoR) and resource consents for the SH2 Dowse to Petone Upgrade works were lodged with the Hutt City Council (HCC) and Greater Wellington Regional Council (GWRC) in 2001. The applications were publicly notified and a public hearing was held in October 2001 before a group of independent Commissioners.
The Hearing Commissioners recommended that the Notice of Requirement be confirmed and resource consents for the project granted subject to various conditions.
The NZTA accepted the Commissioners recommendation on the NoR, but rejected two of the conditions. A number of appeals were lodged against the NZTA's decision and the resource consents. These appeals were resolved by the NZTA without needing a hearing before the Environment Court
The NZTA has obtained the following consents for the project:
- Notice of Requirement (Designation)
- Resource consents from HCC for the construction of the Dowse Interchange and Korokoro overbridge;
- Resource consents from GWRC for land use consents (culverts) and discharge permits associated with the works (eleven consents);
- Resource consent for the small bridge over the Korokoro Stream.