1 May 2013
The NZTA is currently finalising its RMA consents applications to the Environmental Protection Authority (EPA) for the Basin Bridge project. The full application, including supporting technical information, will be made available online when this application has been lodged with the EPA. A map showing the current understanding of the scope of proposed project work is available in our gallery maps section.
- The decision to proceed with Option A
- Key benefits of the Basin Bridge
- Things we considered in deciding to put SH1 on a bridge
- The Tunnel to Tunnel ("T2T") project
The street system around the Basin Reserve currently functions as a large roundabout with signals. About 25,000 vehicles enter from Kent Terrace each day, with nearly 20,000 heading towards Mt Victoria Tunnel. About 20,000 vehicles enter the system from Mt Victoria Tunnel, and 30,000 vehicles travel along Sussex Street.
The streets in this area have several functions: a state highway, a local road, a key public transport route and a key route for pedestrians and cyclists. Congestion is affecting SH1 traffic, local traffic, freight, pedestrians and bus travel. Without intervention, congestion and journey times in the inner city are predicted to increase by up to 75% by 2021.
For example, that means that if we don’t take the right steps to sort this out now, then by 2021 it will take about 16 minutes to from Cobham Drive to Taranaki Street. With the bridge in place, the same trip will only take 10 minutes.
The Greater Wellington Regional Council, Wellington City Council and NZTA agreed in the Ngauranga to Airport Corridor Plan (external link) that the north-south traffic needs to be separated from the east-west traffic around the Basin Reserve. So, following extensive investigations and a community engagement programme in 2011, the NZ Transport Agency has decided to build the Basin Bridge as Option A. This bridge forms part of the Tunnel to Tunnel (“T2T”) suite of inner city transport improvements.
The decision to proceed with Option A
Thorough investigations have shown that the most effective way to separate the north-south and east-west traffic flows in this area is by putting SH1 westbound traffic onto a bridge to the north of the Basin Reserve.
In 2011, the NZTA engaged with the community on two options for this bridge: A (the preferred option) and B. Based on investigations done both prior to and after this engagement, plus the feedback we received from stakeholders and the community during the programme, the NZTA will proceed with its preferred option: Option A. You can learn more about how this decision was made by reading the Paterson to Tory Street Option Assessment Report 2012 (PDF, 1.56MB). If you’d like to learn more about the community engagement programme you can read the Community engagement summary report (PDF, 4.3MB).
Westbound SH1 traffic will travel on a two lane bridge along the northern side of the Basin Reserve. The bridge will be 6 meters above the road (eg Kent and Cambridge Terrace) and 260 meters long and 13 metres wide. The pedestrian/cycle facility will be about 3 metres wide.
Once exiting the Mt Victoria Tunnel traffic will travel above Paterson Street, over Kent and Cambridge Terraces, Dufferin Street and Ellice Street to meet Buckle Street just before the Tory Street intersection.
You can see an artist's impression of the bridge at the top of this page.
Key benefits of the Basin Bridge
- Reduced traffic flows around the Basin Reserve
- Reduced travel times and congestion
- Improved passenger transport and local road journey times and reliability
- Improved freight transport
- Improved connectivity for people using active travel modes (walking and cycling)
- More reliable emergency service access to and from Wellington Hospital
- Improved access and reduced severance to local communities, schools and facilities
- Improved safety for all travel modes (walking, cycling, and vehicular)
Things we considered in deciding to proceed with plans to put SH1 on a bridge
Our decision to proceed with investigating a bridge was based on thorough investigations and a robust selection process. Even though the Ngauranga to Airport Corridor Plan (external link) requires grade separation, we re-considered street-level options, to ensure that a bridge was the most effective solution. We found that the street-level options offered fewer benefits, had a higher level of urban design impacts and were not as good as a bridge in separating SH1 traffic from local traffic. Importantly an at-grade solution would not separate SH1 traffic from local traffic in order to improve the services provided by buses and other forms of public transport between the CBD and Newtown - a key objective of the plan.
We also considered building a tunnel around the Basin Reserve. However, because it had to extend between Paterson and Taranaki Streets to be viable, we discounted it. This decision was based on the complexities of constructing a tunnel through an old swamp, as well as it being considerably more expensive than a bridge.
Since making this decision, we carried out further geotechnical investigations to assess any construction risks associated with building the bridge. Investigations in the low-lying areas around Kent/Cambridge Terrace confirmed potentially liquefiable soils and suggested that ground water was present at a higher level than previously expected. They also showed that we would have to dig much deeper than we originally thought to find solid ground. All these conditions increase the challenges associated with any below-ground construction and make tunnelling in this area even less feasible than previously thought. Read more about why the NZTA decided not to build a tunnel around the Basin Reserve.
The Basin Bridge will best meet the needs of all modes of transport, both now and in the future. Options for the project have always proceeded on the basis that Buckle Street could be put underground should funding become available, the bridge design will integrate well with the Buckle Street Underpass at Memorial Park.
The Tunnel to Tunnel ("T2T") project
At present, Wellington experiences significant congestion, delays and variable travel times on the roads between the Terrace Tunnel to the north and the Mt Victoria Tunnel to the south. Individual projects to address these issues have been in the works for several years, however the NZTA now has the opportunity to bring all this work under one umbrella: the Tunnel to Tunnel improvement project (or “T2T”).
T2T brings together three key pieces of work: the Basin Bridge, Inner-city Bypass Improvementsand the undergrounding of Buckle Street to create Memorial Park. By incorporating these three projects into one, the NZTA will be able to create a much more efficient, seamless construction process than by delivering them separately. By combining the three projects into one package of improvements, we expect to create significant savings, both in time and money, and gain the highest level of benefit from the significant investment being made in this area.