Preparatory work is due to start today on the Onehunga side of a $230 million motorway duplication project across Manukau Harbour, despite uncertainty over foreshore restoration plans.
But the Transport Agency is assuring Onehunga residents it will begin motorway-widening work at each end of a sector between the Mangere bridge and Queenstown Rd in Hillsborough, leaving the foreshore untouched in the middle, pending negotiations over its future.
That follows a decision by the agency's board to open discussions with the Onehunga Enhancement Society and other parties, including Auckland City and the regional council, over a community-based proposal to shift the motorway west to provide a buffer between it and a lagoon on the other side.
The society believes the buffer is needed to provide a corridor for a future railway coastal alignment identified by the Auckland Regional Transport Authority for a potential Southdown to Avondale line, and for utilities such as underground power transmission lines.
Agency acting regional manager Tommy Parker said yesterday that residents should not be alarmed at the removal of small trees, shrubs and topsoil at each end of the Onehunga sector, where the motorway speed limit would also be lowered to 80km/h for project purposes.
He said the contractors would have enough to do there until next year, while the westward shift proposal was considered and resource consents obtained, if his board decided to proceed with it.
Only by about March would it become "critical" to the project to start work on the mid-section through Onehunga Bay.
Supporters of the enhancement society's proposal to shift the motorway include Roskill MP Phil Goff and Auckland City, which has allocated $150,000 for a "master-plan" for harbour foreshore development between Southdown and Hillsborough.
But the city's support is contingent on a three-way funding split between itself, the Transport Agency and Auckland Regional Council, for an 11ha foreshore reclamation plan expected to cost between $18 million and $33 million.
That is additional to an offer by the agency of $10 million for a large pedestrian bridge over the widened motorway and the agency's expected outlay of $7 million to $10 million for the shift itself.
The regional council also wants the agency to consider sinking the motorway into a partly covered trench along the bay, to restore the direct waterfront access lost to the Onehunga community when the road was built in the 1970s.
Mr Parker said his board had yet to make any resolutions about that idea, but it had received a staff report estimating a likely additional cost of $160 million, along with $230 million to the Manukau Harbour crossing duplication project, which reaches from Walmsley Rd in Mangere to Hillsborough.
That could mean doubling the project cost to $460 million.