The bridge crosses the Rangitikei River into Manawatu about 1km east of Mangaweka township.
It was closed for 15 days in 2016 to repair its timber deck but, during repairs, more problems were found.
When it reopened, the weight of vehicles using it was restricted to six tonnes and the speed limit became 10km/h with no stopping allowed.
The two councils then began the process of applying to NZ Transport Agency (NZTA) for funds to build a new $11 million bridge, 30m downstream, and marked the existing single-lane bridge for demolition.
But a recent investigation of the existing bridge concluded the foundations were more stable than thought and met seismic requirements that made it suitable for a footbridge.
John Jones, roading manager for the Manawatu District Council, said the condition of the surrounding rock near one of the piers was in much better condition than initially thought.
On August 5, a public meeting was held at Awastone Mangaweka, where both councils, mayors and members of the public met to discuss the possible retention of the bridge as a footbridge and cycling facility.
Watson said there were a few people who were initially slightly hesitant but by the end of the evening everyone present was in support of retaining the bridge, including repairing and maintaining it for 50 years.
The costs over this timeframe will include repairs to the running boards, decayed timber kerbs and replacing handrails to comply with the building code.
Jones said these works would bring the bridge to an acceptable footbridge standard and extend its lifespan for around 50 years.
The lowest cost option over a 50-year period is to retain the existing bridge rather than demolish it, Jones said.
The current estimated cost of retaining the bridge for 50 years, converted to a Net Present Value (NPV) and using a discount factor of 6 per cent, is $478,000 compared with the NPV cost for demolishing the bridge that sits at $800,000.
However, after 50 years the existing bridge will need to be strengthened at an estimated cost of $4.6 million compared to an estimated demolition cost of $920,000.
"It's a 50-50 call in terms of the cost but we wanted to support the community and what they wanted," Watson said.
The design of the substructure and the approach roads for the new bridge is complete.
"The design of the superstructure is also well advanced," Jones said.
The draft resource consent application document is now complete but the councils are awaiting input from affected parties on land entry and acquisition negotiations are ongoing, Jones said.
He expects the "optimistic" date for calling tenders will be late November, dependent on the consenting process, land acquisition and funding approval.
Watson thanked Taihape councillors Ruth Rainey and Richard Aslett, who are both stepping down from the council, for the work they had done on the project.
