Auckland Harbour Bridge is said to be struggling under increasing freight weight and a decision on what to do needs to be made as early as 2021, George Wood says.
The North Shore councillor says he has been told of some trucks, weighing twice the permitted weight of 45 tonnes, crossing the bridge.
New Zealand Transport Agency says the route for the Waitemata tunnel, earmarked for 2020, should be outlined by the end of this year.
Auckland Council's transport committee was told traffic numbers over the bridge have plateaued since 2008.
But NZTA's regional highway manager Tommy Parker told the committee the bridge cannot take the increased freight loadings, Mr Wood says.
Western and southern commuters would use the tunnel.
NZTA says traffic through central Auckland would continue to use the bridge to and from the North Shore.
The harbour bridge would be "reconfigured to provide for alternate modes - public transport, walking and cycling".
NZTA's preliminary route for the tunnel says it would connect to the "Akoranga bus and rail station" on the northern side and the CBD rail loop on the city-side.
Mr Wood says NZTA is investigating tunnel "alignment across to Victoria Park and their second option of a route that would take traffic up Grafton Gully".
Consultation with North Shore communities will take place post-route designation, Mr Wood says.
No decision on a Stafford St bus interchange to connect to the busway has been made.
- © Fairfax NZ News
Have the new speed limit rules made you change your driving habits?