NZTA begins environmental trial for Northwest Motorway upgrade


The first stage of work to improve the causeway on Auckland's Northwestern Motorway (State Highway 16) is underway with the NZ Transport Agency starting construction today of a trial causeway to test the impact the larger project will have on the immediate environment.

The trial involves building a 50 metre long temporary causeway and carrying out tests in the surrounding Motu Manawa – Pollen Island Marine Reserve. The work will trial the most effective methods for constructing the larger causeway upgrade.

“We’re starting this trial on the causeway so we can get a good idea of the conditions inside the reserve and ensure that the construction footprint is as environmentally light as possible,” says the NZTA’s Acting State Highways Manager for Auckland and Northland, Steve Mutton. “We recognise that this is an important and sensitive area.” 

The $6M trial is scheduled to be completed in July. The NZTA and its contractor, Downer, will focus on monitoring plants and wildlife in the marine area to minimise the impact of building the improved motorway.

A ‘cofferdam’ will be built around the trial area to protect it from tides and to keep the construction area dry while the temporary causeway is constructed. The cofferdam will be constructed from shipping containers covered with a waterproof sheet and will be removed once the temporary causeway is completed.  The temporary causeway will sit 1.5 metres higher than the adjacent motorway.  It will be constantly monitored by the NZTA until it is eventually absorbed by the main causeway upgrade.  

People will need to take care when driving past the trial site and keep to normal motorway speeds. They will be able to see a large crane and machinery from the motorway.  A bus shoulder lane has been removed for the work.

“Getting the right approach and methodology is important to carry over to the main project which will raise and widen the causeway between Great North Road at Waterview and the Rosebank and Patiki interchanges, and eliminate flooding onto the motorway which occurs during king tides,” Mr Mutton says. 

The NZTA has invited expressions of interest from consortiums interested in the larger 4.2 kilometre long $270m Causeway Upgrade project between Waterview and Te Atatu.

“We’re looking at announcing the successful consortia in September and aiming to get going on construction early next year, saving time and money in the long term by having completed the testing work already”, Mr Mutton says. 

The project also includes upgrading the Rosebank and Patiki interchanges, providing treatment to stormwater runoff, widening bridges and improving the Northwestern Cycleway and pedestrian facilities along the route. It is expected to be completed in 2017.

The causeway upgrade is part of a suite of projects in the Western Ring Route – Road of National Significance, prioritised by the Government to support growth and economic development in Auckland. The alternative route to SH1 will improve connections between Manukau in the south, Auckland International Airport, Waitakere in the west and the North Shore, and ease congestion on the Auckland Harbour Bridge and the central city.

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Causeway trial

Causeway trial diagram