He branded the plan "fantasy stuff".
Genter was inclined to agree, and questioned where Tamihere expected to get the money from.
"I think that Mr Tamihere has demonstrated that he has a very poor understanding of how transport systems work and also how Government funding works."
The project would be inefficient and not what Aucklanders want, she said.
"Aucklanders really want a rapid transit system, not heaps more traffic in the city centre."
Genter's comments come after Tamihere and Goff went head-to-head in an NZ Herald debate last night.
Tamihere accused Goff of introducing four of the eight taxes on Aucklanders' rates bills while Goff repeatedly accused Tamihere of coming up with policies he knows he cannot deliver.
"Everything John says is factually incorrect. He makes it up as he goes along," he said.
Tamihere proposed turning the existing Harbour Bridge into a two-level superstructure – with 10 lanes for cars on the lower level and four rail tracks and walkways and cycleways on the upper level.
The superstructure replacement for the 60-year-old bridge is the first transport policy announced by Tamihere, who is challenging Phil Goff for the mayoral chains at October's local body elections.