Mr Campbell was responsible for the branch line when the track was lifted in 1999 and made "the conscious decision" to retain the rail corridor and its designation for use as a railway line, even though there was no demand then.
But, through an error, the designation was not rolled over by the Waitaki District Council when it reviewed its district plan in 1993.
OnTrack wants that corrected, which is being considered by planning commissioner Allan Cubitt at a three-day hearing which started in Oamaru yesterday.
Holcim regarded rail as an "important consideration" in its plans for the plant, Holcim legal counsel Peter Christensen said.
If it were not available, Holcim would have to rethink how it would distribute cement from the plant, most likely using trucks.
At the start of the hearing, Mr Cubitt warned those making submissions to stick to the rail designation, and not debate the $300 million cement plant proposed by Holcim (New Zealand), near Weston.
He would not relitigate the Holcim decision - resource consents having already granted by the Otago Regional and Waitaki District Councils for the cement plant, but appealed to the Environment Court.
There may be some issues related to the Holcim plant, but these had to relate to the effects of the designation and the railway corridor alone, Mr Cubitt said.
OnTrack consultant planner David Collins, of Collins Consulting, said the dominant fact in submissions appeared to be that reopening the branch line was associated with Holcim's cement plant project.
Some people making submissions had taken the opportunity to "derail" the Holcim project.
It would be inappropriate for the hearing to become an inquiry into the merits of the cement plant, already exhaustively investigated and to be scrutinised by the Environment Court.
It should be limited to reopening the rail corridor, Mr Collins said.
OnTrack's legal counsel, James Gardner-Hopkins, said the rail designation was mistakenly left out of the proposed district plan and the current notice of requirement was effectively a roll-over of the former designation.
Much of the public interest in the designation came from Holcim's proposal.
While the cement plant was relevant in terms of the use of the line, any broader consideration of the proposal was irrelevant, he said.
Mr Campbell estimated it would take six to eight weeks to complete the work necessary to reopen the line if the cement plant were built.
There would likely be four train movements a day, Monday to Friday, and two on Saturday - equivalent to 170 truck movements a day.
Dunedin locomotive engineer Kevin Martin estimated the trucks would use 6000 to 8000 litres of fuel, compared with 1500 litres for the equivalent trains.
Mr Campbell identified safety at level crossings and noise as the key effects from reopening the line.
All five level crossings would have flashing lights and bells and there would be a hiking speed limit on the rail line.
Noise was considered by OnTrack to be "entirely acceptable", Mr Campbell said.
