Producing a detailed design for two-way traffic in George St would force a delay in construction, council staff said.
Developing a design to incorporate "two-way flexibility" could take four to eight months, they said.
The estimates are included in a report to be considered by the Dunedin City Council’s infrastructure services committee next week and the report’s content appears to present significant barriers for any mid-project revision.
They include redesigning the paving layout, moving furniture, rearranging car parking and creating zones that would be clear of significant obstacles, such as garden beds.
The council decided in 2021 to make three blocks of George St one-way as part of a drive to make it much more pedestrian-oriented, but the matter has been contentious, even as work progressed.
Dunedin Mayor Jules Radich campaigned last year for a review and by the end of the year the council had voted eight to seven to look into "how flexibility can be incorporated into the remainder of the project to minimise future expense if modification is deemed necessary".
Council staff took this to mean allowing for 30kmh two-way traffic in the Golden Centre and Edinburgh Way blocks in the future. The one-way Farmers block, between Moray Pl and St Andrew St, has essentially been completed.
Council staff estimated there would be costs of between $300,000 and $500,000 to develop a design to incorporate two-way flexibility and this would take four to eight months to complete.
Construction would have to be delayed and this might cost between $750,000 and $1 million a month, council staff said.
Their report said staff were unable to give accurate costs of changes to infrastructure to incorporate flexibility until two-way design work had been completed.
"For example, detailed design would need to confirm the location of below-ground infrastructure in a new roading configuration and then where and how duplicate infrastructure at intersections could be accommodated."
The project remains within budget and is due to be completed by September next year.
It will continue to be delivered in line with a detailed business case, "unless the council directs otherwise".
The George St upgrade forecast spend is $51.3 million.
Waka Kotahi NZ Transport Agency is contributing $12.1 million of the total.
