Replacement for Whanganui’s Dublin St Bridge still years away

The bridge opened in 1914 and spans just over 300 metres. Photo / NZME

It could take a decade for Whanganui’s Dublin Street Bridge to be replaced, and tolling is an option if the Government does not provide funding.

Whanganui District Council civil engineer Thorbjoerg Saevarsdottir told the council’s projects and grants committee that work on a detailed business case for a replacement could take two years to complete.

Once finished, it will be presented to NZ Transport Agency Waka Kotahi (NZTA) for funding consideration.

“Basically, that [business case] looks at ‘do we need a bridge, do we not need a bridge?, traffic modelling, etc’,” she said.

“We can probably prove we need the bridge but that’s part of the feasibility. We don’t want another Bridge to Nowhere.”

The bridge opened in 1914 across the Whanganui River and spans just over 300 metres.

At present, it has a vehicle weight limit of six tonnes, meaning it is shut to heavy vehicles.

A report from Saevarsdottir said the bridge had passed its use-by date and was “extremely vulnerable”.

She told the committee there were too many variables to put a final cost on the project.

In the council’s Long-Term Plan for 2024-34, it is estimated to cost $69 million.

“If we can use the existing piers, it’ll cost a whole lot less than if we need to construct a whole new bridge,” she said.

Piers are structures that extend to the ground or into the water, supporting bridges and transferring the load to the foundations.

Council chief infrastructure officer Lance Kennedy said the current work was a feasibility project “not a build project”.

“It’s a decade away from a build, if at all,” he said.

NZTA has a cost split with the council of 62%-38% on projects it agrees to fund.

Saevarsdottir’s report said if the agency declined to partially fund a new build, alternative funding sources may be necessary to advance the project.

“This includes options of tolling or user pay considerations in some form.”

The bridge currently has a vehicle weight limit of six tonnes. Photo / NZME

Councillor Rob Vinsen said there would be public interest in that and asked if there were examples around the country.

Council transport manager Mark Allingham said the harbour bridge linking Tauranga and Mount Maunganui created a lot of controversy.

“They built it with tolls and kept tolling it for a long time after the bridge was paid for,” he said.

“That revenue stream kept coming into council.”

While it was a long way in the future, those options had to “be looked at and considered as we go along”.

Allingham said one model was a DBOM – design-build-operate-maintain.

“Someone else could build the bridge, which is wholly or partially funded by them, and they would operate a tolling system over a period of time.”

Councillor Philippa Baker-Hogan said replacing the bridge had been a topic for as long as she had been on the council (since 2006).

“Comments around it being past its use-by date and being extremely vulnerable, [they] kind of cause alarm,” she said.

“When do you expect to get a better timeline update to this committee and council?”

Allingham said he would report to the committee monthly “and continually tell you as things happen and as things develop”.

He said because the bridge was posted (restricted), it was inspected more frequently than others in the district.

“It has extra vigilance as well as any maintenance.

“All works are being carried out to ensure the bridge is not only safe now but will continue to operate and function well into the future.”

According to the council’s Long-Term Plan, maintenance work to extend the life of the bridge by 20 years is expected to cost $29.2 million over that period.

“It is also likely that the bridge would need to be downgraded from a maximum weight of 6 tonnes to only 3.5 tonnes for the last five years,” it said.

Demolishing and removing the bridge and reconfiguring the road “to manage the loss” would cost about $10 million.

Saevarsdottir said any designs for a new bridge would not begin until the detailed business case had been given to NZTA and funding was approved.

Mike Tweed is a multimedia journalist at the Whanganui Chronicle. Since starting in March 2020, he has dabbled in everything from sport to music. At present his focus is local government, primarily the Whanganui District Council.