For seven years, Mrs Jones has been concerned walkers were forced on to the road to cross busy State Highway 87.
The spot was especially dangerous for mothers with small children, and the elderly, some of whom turned back rather than negotiate the road.
She said she had been asking the Otago Regional Council for years, but little happened.
"I was like a dog with a bone."
It took the co-operation of the New Zealand Transport Agency (NZTA), the Otago Regional Council and the Dunedin City Council, about 18 months ago, to advance matters, she said.
The regional and city councils share responsibility for the walking track.
Fellow Mosgiel resident Geoff Neilson helped things along, Mrs Jones said.
However, Mr Neilson was quick to give Mrs Jones the credit, saying it was his friend's "persistence" that made the underpass possible.
A "hump" on the bridge created a blind spot, making it all the more dangerous, he said.
NZTA Coastal Otago area manager Roger Bailey said the concrete path should be finished by the end of this week, depending on the weather.
The $25,000 path is designed to withstand flooding, Mr Bailey said.
