There are concerns any traffic time savings created by the $120 million Baypark to Bayfair project could be eclipsed by growth within a decade.
The Tauranga City Council has raised serious issues around capacity and gaps in public transport, pedestrian and cycling links in the project with the New Zealand Transport Agency, and chief executive Marty Grenfell is calling for a "pause".
Baypark to Bayfair, also known as Baylink, is the biggest transport project in the Bay of Plenty.
Construction started in 2017 to build two-lane flyovers on Maunganui Rd/State Highway 2, bypassing the Baypark and Bayfair roundabouts and connecting to State Highway 29A.
The work was expected to finish in late 2020.
This month the agency announced it was scrapping plans to build a new pedestrian underpass under Maunganui Rd at Bayfair after estimated construction costs blew out to $33m.
The decision stoked the ire of local pedestrians and cyclists, with talk of petitions to Parliament and protests.
The lack of consideration for buses and other modes of transport in the project also had the council worried.
The issues were raised in a meeting of the council's Urban Form and Transport Development committee yesterday.
The meeting heard that new modelling by the council showed there could be a drop in Baylink's "level of service" by 2031, essentially meaning the travel time savings it was expected to provide were possibly already being eroded.
Council growth and infrastructure manager Christine Jones told the Bay of Plenty Times after the meeting there were many variables the model could take into account, and not all scenarios showed a drop in the level of service.
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Modal shift - more people biking, bussing or walking instead of driving - and changes in other parts of the wider transport network could also influence the impact of Baylink on travel times, she said.
Ross I'Anson, the transport agency's acting director of regional relationships for the Central North Island, presented to the meeting, fielding questions from councillors about the underpass decision.
He said the agency was looking at other options for pedestrians and cyclists, including an overbridge.
L'Anson and Grenfell met again after the meeting.
In a follow-up email to the agency, Grenfell said the two organisations needed to work together to reassess the project.
In particular, they should take stock of current public views and what changes to the project might be needed to ensure it would meet the current Government's transport priorities.
"We need to pause, engage and re-set these critical factors within the project," he said.
In other emails, Grenfell said he was concerned about "plug[ging] on with constructing transport corridors that won't serve us well into the future" and about potentially having to retrofit options for buses and other modes of transport.
L'Anson told the Bay of Plenty Times the agency would talk to the council and other partners about the latest information from modelling and what it meant for the sub-region.
It had heard the concerns of the community about the underpass and was working through possible alternatives, including an overbridge - which could be a separate project.
"Five years on from when the Baypark to Bayfair Link project was first scoped, the rate of growth throughout Tauranga city has grown faster than anyone predicted.
"This unprecedented growth will have an impact on the transport network throughout the city.
"Growth in our population and our economy means we need to better plan for the future and help shape our cities and towns in a way that enables people to move around safely and easily."