Opponents of the Basin Reserve flyover have been given a big boost, after independent experts backed some of their objections.
The NZ Transport Agency has spent 18 months preparing its resource consent case for the highway flyover, 20 metres north of the Basin, to present to a board of inquiry hearing that will begin today.
But a new report released by the board's advisers, Abley Transportation Consultants, suggests that some of the red flags raised by opponents of the $90 million project have not been adequately addressed.
The report has renewed opposition hopes that the flyover can be stopped, despite construction being scheduled for later this year.
The board also appeared concerned by the disagreements among experts on both sides of the debate. It has summoned all experts to a special meeting on Wednesday in the hope they will narrow down their differences before the board hears evidence about traffic and transport issues.
Abley has now produced two peer-reviews of evidence that will be presented at the eight-week hearing - one assessing the transport agency's evidence and another assessing the evidence submitted by everyone else.
The latter report, released last week, said the agency had done a "robust" assessment of alternative solutions to the Basin's congestion woes.
But some submitters raised "valid questions" about whether a revamp of the status quo would be enough, given that most of the Basin's congestion would be solved by the Buckle St underpass, which is already under construction.
The underpass has removed the traffic lights at the intersection of Buckle St and Tory St where vehicle queues around the Basin often begin.
Abley also shared the concerns of Cycle Aware Wellington, who say the flyover's shared walking and cycling path is too narrow and too dangerous, and will not accommodate the growing number of cyclists in the capital.
Abley supported a 4.5m-wide path rather than the 3m-wide path proposed by the agency.
The report also cast doubt over the reliability of the transport models used to predict travel time savings.
But Abley disagreed with a number of the submitters' views. Notably, they doubted that improved private vehicle times would encourage people away from public transport.
In documents submitted to the board, the transport agency's transportation expert, David Dunlop, said revamping the existing roundabout was a "sub-standard solution" that would need to be addressed again in a few years.
The walking and cycling path had been designed to meet the agency's guidelines, and if people felt unsafe there were alternative routes, he said.
He defended the quality of the transport models used, saying they had also been used in planning for Transmission Gully and the Kapiti expressway, which were granted consent.
Save the Basin campaign spokeswoman Joanna Newman said the group had always felt its experts would present a good case, and the Abley reports appeared to back them.
"We feel that this peer review supports our view and all of our expert evidence."
Wellington Central MP Grant Robertson said reports showed the flyover's resource consent was by no means a certainty.
"In my view the flyover is still a flawed project."
- The Dominion Post