As evidence, she cited a Mt Eden management plan from 2007, which said erosion was "apparent in observations of slips, soil creep, and the filling and shortening of terraces".
But it did not link this damage to vehicles, instead attributing it to "natural processes", pedestrians, excavation for utilities, earthworks, and grazing stock. Stock are already banned from the summit.
Mr Seymour said: "Clearly, car-induced erosion is either not occurring or is not a factor in the authority's move to ban cars - a fact that contradicts the erosion-focused narrative."
Albert-Eden-Roskill councillor Christine Fletcher would not comment on Mr Seymour's erosion questions. But she said she was aware the ban had caused distress to people concerned about access. She had been assured vehicular access to the summit would not be removed until alternatives were in place.
Mr Seymour said the authority had failed to consult with representatives of Auckland ratepayers, or Mt Eden's typical visitors.
Authority chairman Paul Majurey did not return calls yesterday.