The Whangarei/Auckland railway line could be mothballed for an indefinite period from next year, after talks KiwiRail plans to have with the region's businesses and local authorities.

KiwiRail CEO Jim Quinn delivered the facts about the route to yesterday's monthly meeting of the Northland Regional Council.

A final decision on mothballing the route or keeping it open is up to a year away.

He told councillors the cost of running the trains on the route was almost exactly the same as the service was earning ($8 million to $9 million) and that the route was "a barely used asset in terms of the amount of investment".

He stressed that KiwiRail would keep any railway land.

His job to make KiwiRail viable nationwide and that meant addressing the issue of uneconomic routes.

"We are working through these issues with the four 'most stressed' routes in the country. Northland is one of the four," he said.

The Auckland/Northland line presented the most complex issues although the Dargaville line was "less robust". There were 13 tunnels between Auckland and Whangarei and six needed work space for larger containers.

"These containers just won't fit through the holes in the hills," Mr Quinn said.

There were two return week-day freight services and occasional passenger charter services between Auckland and Whangarei; and local services within Northland for forestry and dairy customers.

He confirmed the obvious - mothballing the route meant the Marsden Pt rail link was out of contention as well.

KiwiRail was at "the bread and water stage and we can't even think about jam and cream yet."

Mr Quinn said KiwiRail wanted to engage with the Northland community to see if "we can flush any revenues ... the commercial possibilities around the region as well as the probabilities. This is a collaborative thing. We need to work out what these are and we will look at all this information at about the same time next year."

He said when routes were taken out of service they were maintained for about five years.