Expert praises John Tamihere's 'out-of-the-box' bridge plan

An infrastructure expert does not believe John Tamihere's Harbour Bridge plan is feasible, but likes his "out-of-the-box" thinking.

The Auckland mayoral candidate wants a new structure built atop the existing piers, with 10 lanes for cars and a second level for cyclists and trains.

But Infrastructure New Zealand CEO Stephen Selwood doubts it's possible, with major logistical questions hanging over the plan.

"How do you maintain the crossing during that whole process? At some stage you're going to have a do a change, and that's going to be quite disruptive."

But he is commending Tamihere for being ambitious.

"To be honest, I can't see it being feasible. But it's good to see out-of-the-box thinking, and we do have to address how the North Shore grows."

Tamihere hasn't costed the plan. Incumbent Mayor Phil Goff says it'll be upwards of $10 billion, and would bankrupt the city.

"It's dumb," he told Newshub.

Selwood says it's not just the bridge Tamihere will need to pay for - other connections have to be taken into account.

"We all know that Spaghetti Junction on the southern side has not got much capacity in it, if any. You'd have to widen the Northern Motorway as well. And where does the light rail corridor go?"

Tamihere has yet to discuss the proposal with the New Zealand Transport Agency, which runs the motorway network the bridge is a part of. But he doesn't see that as a problem.

"Who cares? They do as they're told. They're bureaucrats."