Organisers of an 8000-signature petition to restore rail services to Onehunga say the suburb's rusting 3.4km branch line could be reopened for less than the cost of a motorway offramp.

Campaign for Better Transport convener Cameron Pitches said winning funds for rail projects was like getting blood from a stone, as these were given far closer scrutiny than new roads.

He presented the petition to the Auckland Regional Council last night, saying a new multimillion-dollar offramp carrying traffic from the left-hand side of the Southern Motorway to Nelson St under the council's headquarters had made no significant dent in Auckland's traffic congestion.

The old disused right-hand ramp was to remain in place "presumably as an everlasting monument to how easy it is to get funding for roading projects", he said.

"Meanwhile, the Onehunga line has deteriorated so much that no train can get to Onehunga on it."

Mr Pitches cited a 2004 report to the regional council estimating the line could be reopened for as little as $3.5 million, including three rudimentary stations, or up to $10.7 million in a worst-case scenario of having to replace all its tracks to Penrose.

Yet the project had, despite council support, failed to get into a draft 10-year passenger transport network plan of the council's Auckland Regional Transport Authority subsidiary.

He bemoaned the fact that the Government rail agency Ontrack had stopped allowing the line to be used for special charter trains, including one which his organisation hoped would have carried the petition to central Auckland last night, for fear it had become too unsafe.

The petition has support from two Government members, Defence Minister Phil Goff as MP for Roskill and former Transport Minister Mark Gosche as MP for Maungakiekie.

It is also supported by the Auckland City Council and Maungakiekie Community Board.

Although transport planners using computer modelling predict only 340 passengers would catch trains from Onehunga during each morning traffic peak by 2016, Mr Pitches said no one could have foreseen the tremendous popularity of new rail services around the region.

"We believe that having talked to 8000 people around Onehunga we have a better idea of how viable it is rather than looking at a spread sheet," he told the Herald.

Reopening the line, which was built in 1873 and closed to regular train services a century later when cars became Auckland's dominant means of commuting, would enable Onehunga residents to reach Britomart in 19 minutes.

This compared with trips of often an hour or longer by bus at peak times, and was also likely to be significantly faster than commuting by car. Rising fuel prices were also overshadowing transport patronage predictions.

Regional council chairman Mike Lee undertook to relay the petition to the transport authority's board and to ensure its message was included in a council submission on the authority's passenger network plan.

He said after the meeting that Auckland's rail network had been badly neglected while under private ownership and the Government had a responsibility to ensure such a valuable taxpayer-funded asset as the Onehunga line was not squandered.

Ontrack spokesman Kevin Ramshaw said his organisation could not make decisions about upgrading lines without a funding source, but noted that the regional transport authority had been reviewing options and the level of work required.