Transport Agency contractors are to build a dummy causeway in an Auckland marine reserve as a trial run for a major upgrade to the Northwestern Motorway.
The agency yesterday announced its award of a $6 million contract for the 50m temporary causeway, which will be built between next month and June beside the motorway in the Motu Manawa-Pollen Island Marine Reserve.
That will be a practice run for a $270 million project to widen and raise the existing causeway by about 1.5m between Waterview and Te Atatu to cope with rising sea levels and extra traffic from a new $1.4 billion link with the Southwestern Motorway.
Agency northern region highways manager Tommy Parker said the temporary structure would be built on the seaward side of the Northwestern Motorway, ahead of the main project, which is expected to take four years to complete from early 2013.
He said that because the existing causeway had been sinking since it was built in 1952, the agency needed to get "a better feel" for geotechnical conditions before the upgrade began.
That would provide a better-informed contracting process for the upgrade.
He said the trial causeway could be built within terms of a consent for the upgrade project granted by a Government-appointed board of inquiry.
The upgrade of the existing causeway will provide stormwater treatment from the structure for the first time and Mr Parker said his organisation had advised the Royal Forest and Bird Protection Society about the trial structure.
Mr Parker also confirmed yesterday that a contract had been signed with a consortium led by Fletcher Construction for work to start on the 4.5km Waterview motorway section, of which just over half will be tunnelled.