Opponents of a flyover near Wellington's Basin Reserve say it would be a "brave" judgment to overturn a decision to deny the project's resource consent.
A board of inquiry denied the $90 million project resource consent after a lengthy hearing last year, but the New Zealand Transport Agency (NZTA) has taken an appeal to the High Court in Wellington.
The agency's lawyer, Matthew Casey, argued that the board misinterpreted the Resource Management Act and applied a wider definition of heritage than was required.
However, the lawyer for the Save the Basin Campaign and Mount Victoria Residents Association, Matthew Palmer QC, said the agency had made up its mind some time ago.
"It saw a problem and it determined to fix them once and for all with a big bang solution.
"And from my clients' perspective that is the solution which the agency has stuck to determinedly, and they now continue to think that they are right in their solution and find it difficult to accept the board of inquiry's report."
Mr Palmer said the board was exposed to many experts and submissions and to overturn the decision based on the facts would be a brave judgement by the court.
Wellington City Council said the board of inquiry's decision to deny the resource consent for the flyover could undermine the integrity of its district plan.
The council's lawyer, Kerry Anderson, said the board took into account matters that it should not have.
She said the district plan was a rule book that recognised and protected heritage, but the Basin Reserve was not a listed heritage item and the board was not entitled to elevate it as one.
Ms Anderson said this had resulted in the Resource Management Act trumping the district plan, and brought into question whether the plan could be relied upon.