The New Zealand Transport Agency has been looking at ways to finish the track, but some sections are narrow, with little space between the railway line and State Highway 88 for a cycleway.
Otago Southland regional director Bruce Richards said while it was possible to build the cycleway, options for some sections were too expensive.
On some sections, insufficient users would not justify the costs involved.
"Pinch points", where there might be a headland high above the road which needed excavating, or where the roadway would need retaining walls to widen it, would be expensive to address.
"The railway line is a constraint. There have been discussions with OnTrack, who are prepared to allow some adjustment to the position of the tracks to provide additional width for the walk and cycleway," Mr Richards said.
Shifting the tracks on their existing formation would not be very expensive, but if reclamation work was needed, the cost would be a lot more, he said.
No further work would be done on the cycleway until consultation with key stakeholders and the public about options for the route was finished.
Consultation was planned to begin within the next few months.
The cycleway presently ended at Maia.
Continuing it to St Leonards was likely to be the next section constructed, although priorities would be set after public consultation.
Any further work would depend on the availability of funding and whether the work became part of the three-year land transport programme in Otago, Mr Richards said.
The transport programme was drafted by the Otago Regional Transport Committee, which comprised one representative from each of the Otago city and district councils, three from the Otago Regional Council, Mr Richards, and six community representatives, who did not have voting rights.
Public submissions on the draft 2009 to 2012 programme close next Friday.
The present 2.5km cycleway was built in two stages.
The first 1.2km section cost $220,000 and the second 1.3km about $300,000.
It was estimated extending the cycleway to Port Chalmers would cost more than $5 million.
