Grafton Gully will go 5m deeper if the newest plan for the motorway link to Auckland's ports goes ahead.
Transport planners have been displaying their latest scheme for ending holdups in Stanley St and The Strand to local residents and businesses vehemently opposed to considering the other option ofan elevated highway.
The idea of a 5m-deep "trench" - running to the west of Stanley St and cutting out its dogleg intersection with The Strand - was born out of consultation with local people late last year.
However, the four-lane sunken highway from Spaghetti Junction would cost up to a third more than the $70 million viaduct, partly because of engineering problems of going below the water table.
A Hobson Community Board member, Stephen Goodman, said last night that the new scheme was the most popular with Parnell people.
The viaduct and another proposal, widening Stanley St to six lanes, are also still on Transit New Zealand's drawing-board.
Mr Goodman said: "Given that we have to do something with that road, I believe [a sunken highway] is the best option of those that have come forward so far. It gives the traffic flow advantage of the viaduct without having the visual impact.
"While it might be slightly more expensive, it has got to be something there for the next 20 years."
Transit will make its choice in June. David Philip, a Beca Carter senior transport engineer working on the project, did not think the motorway authority would simply pick the cheapest option.
"[The sunken highway] would not be a starter [based on cost alone], but it is still being considered at this stage," he said.
While the viaduct option had received the most support from road users and those not living in the area, it was the most unpopular with locals during the consultation last year, he said.
Widening Stanley St and The Strand would not achieve the goal of separating the local and arterial traffic, Mr Philip said.
The three options will go before Auckland City next month.
