Transit NZ was accused yesterday of "quarantining" the country's second-fastest growth area - Rodney District north of Auckland - against further development.

Rodney Economic Development Trust executive Mike Smith hinted at taking court action against the roading agency as he listed 16 projects he claimed it was blocking in its anxiety to protect the state highway network from extra local traffic.

The stymied projects ranged from a cultural tourism venture at Te Hana in the district's north, to a "knowledge economy" zone at Silverdale and a lavender farm and processing plant at Dairy Flat.

"Rodney is now effectively quarantined from future development," Mr Smith declared in a submission to a Transit panel holding hearings in Auckland on the agency's 10-year state highway forecast.

"Economic development within the zone has been brought to a standstill."

Mr Smith said exports with a potential annual value of $253 million, including lost tourism opportunities, were being jeopardised by Transit's early intervention in planning applications.

That meant losing more than 6000 would-be jobs in a district where a growing population was increasingly forced to commute to Auckland for work - down the congested Northern Motorway.

He said only 15 per cent of the Silverdale economic zone was now likely to be developed, because Transit was refusing to spend $5 million on ramps to connect it to the motorway from an existing bridge.

Also at risk was a four-year effort to entice a United States company to build a factory in Rodney, rather than Australia or South Africa, to supply more than $16 million in annual exports to South Pacific customers.

"As their proposed site is on a connector road, they have put their options on hold as they expect opposition from Transit NZ," said Mr Smith, whose organisation is contracted to implement the district council's economic development strategy.

He also accused Transit of denying a would-be developer of a lavender farm and processing plant at Dairy Flat her right to natural justice by blocking a consent application before it could reach a planning hearing.

He told the Herald after the hearing that the district council saw no point in holding a hearing as the venture needed access to State Highway 17 and Transit could, as the road's owner, simply block permission for any enabling work for a traffic connection.

Transit has written to the applicant's planning agent, saying the 40 traffic movements an hour expected to be generated by the project at peak times was unacceptably high "in an area that is already under development pressure".

It feared that if it accepted the project, other small business entrepreneurs would expect similar treatment and the cumulative effects "would seriously deteriorate the safety and transport function of this route".

That prompted an email from planning consultant Shane Hartley to Mr Smith saying Transit had clearly assumed the role of "a new national land-use planning authority - the first since the Ministry of Works and Development ..."

Transit regional manager Richard Hancy, one of two officials on the hearings panel, said afterwards his organisation was spending plenty of time with the council on trying to resolve planning issues at an early stage.

He said Transit was consenting to "something of the order of" 90 per cent of planning applications lodged in his region from Auckland to Cape Reinga.

He pointed to what he says was a successful effort by Transit to resolve traffic issues associated with the Snow Planet attraction overlooking the motorway near Silverdale.