KEY POINTS:
Business and motoring organisations are pushing for wider motorway tunnels than the $1.89 billion twin set which Transit NZ is proposing for Waterview on Auckland's western ring route.
Submissions from both the Auckland Business Forum and the Automobile Association have called for tunnels large enough for three lanes of traffic in each direction, instead of Transit's preferred option of two-lane structures.
Transit says it considered whether to build a pair of three-lane tunnels for $2.14 billion, but feared that making them so big would put unacceptable congestion pressures on other parts of its motorway network.
Although it intends widening the Northwestern Motorway causeway between Waterview and Te Atatu to four lanes in each direction, it says half of that capacity will be for traffic headed to or from central Auckland, leaving the other two lanes for vehicles using the 3.2km tunnels along a 4.5km route between Waterview and Mt Roskill.
But the AA says in its submission that confining the tunnels to two lanes each way was short-sighted from both economic and infrastructure points of view.
Doing so "will certainly deliver network capacity problems for future generations of Aucklanders," it says.
The association also opposes a suggestion by Transit that it may have to toll the new Waterview Connection, once it opens by 2015, to control traffic volumes running through the tunnels.
Spokesman Simon Lambourne said yesterday that Transit had only one chance to ensure the new link was "future-proofed", unlike a surface-level motorway to which lanes could be added as traffic volumes grew.
He said the extra $250 million cost for larger tunnels should be weighed up against estimated annual economic benefits of $840 million from completing the western ring route.
Despite Transit's fears about causing an imbalance to its wider motorway network, the business forum says other parts of the western bypass are being widened to three lanes, including State Highway 20 south of the proposed tunnels.
It says the $230 million Manukau Harbour crossing duplication project goes even further in providing for four lanes of traffic on each of two Mangere bridges.
"We suggest a twin three-lane tunnel would provide immediately a lane option for improved affordable public transport and also provide added safety features with a full stopping shoulder, which is not in the proposal as it now stands."
The forum's submission, in its chairman Michael Barnett's name, notes that Transit's own traffic modelling indicates the capacity of the tunnels of about 4000 vehicles an hour in each lane would be reached within 10 years of operation.
Transit principle project manager Clive Fuhr acknowledged yesterday that it would not take long for the tunnels to fill up, and that travel demand restraints would therefore be needed to reduce underground congestion and any associated build-up of vehicle fumes. But he said three-lane tunnels would not take much longer to become congested in the absence of management measures, particularly if volumes of traffic using them were too heavy for adjoining sections of motorway.
Mr Fuhr noted that the motorway extension through Mt Roskill, just to the south of the proposed tunnels, was being built with just two general traffic lanes in each direction although with bus "shoulders" along their edges.
Transit's board is likely to consider submissions on its preferred Waterview option next month.
