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The work, which will include reclamation of up to 20m of harbour in some areas, will also feature artwork the public is being asked to choose, on a raised section at Roseneath.
The agency announced in May last year the final 5km section of the path would be funded, following a series of delays.
The cost of the project had blown out from up to $10million to closer to $20million to $25million.
Most of the extra costs centred on the route through the steep Roseneath peninsula.
The work will be funded by the NZ Transport Agency through the national land transport programme.
It is part of a long-term plan to have a cycleway running from Taiaroa Head to Aramoana.
In December the NZTA decided to combine a contract for the cycleway-walkway with another for safety improvements on SH88, after no acceptable tenders were received for the latter job.
NZ Transport Agency project manager Jason Forbes said the design for the cycleway-walkway was complete.
The NZTA had attempted to have a 3m-wide sealed path throughout, but there were "a couple of small pinch points".
One of those was where the path travelled under a rail overbridge near Port Chalmers, where it would be about 2m wide.
It would include a 610m boardwalk at Blanket Bay, reclamation work at St Leonards, where the rail track would be shifted, and in the last half of Blanket Bay.
There would be "substantial reclamation" in Mussel Bay.
Space was needed for the path, and for KiwiRail to install dual tracks in future, meaning at some points the reclamation could go up to 20m into the harbour.
Mr Forbes said he expected to call for contracts shortly, though when they would be signed off was anyone's guess.
The plan was to get work started by the middle of the year.
"I would still say within the next couple of months," he said of his hopes for work to begin.
The contracting market was still tight, but he hoped the scale of the project would attract firms from outside the region.
"We're expecting this one will be pretty well received, and the contractors are hungry."
The agency has asked for feedback on a plan to add designs to the cycleway-walkway at the Roseneath cutting.
Work there required a steel post wall above the road with pre-cast concrete panels, which provided "a blank canvas".
The NZTA had engaged Dunedin artist Simon Kaan to develop four possible concepts for the panels, and had called for feedback on its website by Friday, April 19.
Mr Kaan's designs are inspired by a guardian taniwha in the South Island known as Matamata.
Mr Forbes said the agency would look at the numbers who liked each work, though would also consider comments before making a final decision.