Companies seeking rich productivity gains from heavier trucks on selected routes have shown unwillingness to pay extra costs to local councils.

But Transport Minister Steven Joyce is telling ratepayers not to quibble, saying all will benefit from potential productivity gains of $250 million to $500 million a year from allowing trucks to carry loads of up to 53 tonnes under a proposed new permit system.

Only one of 14 companies which answered a survey question on cost-sharing was prepared to pay extra to local road controlling authorities, on top of Government road user charges based on vehicle weight.

Although two reserved judgment, the rest were unwilling to pay extra, most believing road user charges to be adequate. Their views were contained in a report prepared for the Ministry of Transport and former Transit NZ in 2007, but made public under the Official Information Act only after their identities were deleted on commercial grounds.

The report was issued to the Herald after groups such as Local Government NZ and the Campaign for Better Transport complained of a lack of public evidence to support the minister's prediction of economic gains, and scant analysis of costs.

Road Transport Forum chairman Simon Tapper, of Auckland-based Tapper Transport, said the responses did not mean his members were unwilling to pay their way. But they did not want to be lumbered with two types of payment, one to local councils and the other to the Government, under proposed rule changes for which the ministry is assessing 285 submissions.

"We'll pay our way, but we'll pay it to one body and it's up to the politicians how it gets divided up," Mr Tapper said. "We don't want a scenario where we think we're paying our way through our road user charges then the RCAs [road controlling authorities] are sticking their hands up for more."

Local Government and the Traffic Institute fear ratepayers will be exposed to heftier costs for repairing local roads, because user charges on heavy vehicles cover only half the bill through the national land transport fund.

Mr Joyce confirmed that likelihood in a speech to the institute's annual conference in Auckland, but said ratepayers would also share the benefits "of more vibrant economies".

"The people who transport our goods to markets, the farmers, the manufacturers ... they are the people who pay New Zealand's way in the wide world," he said. "They pay the wages of the people and pay for the services of the people who pay the rates in our communities."

But institute president Andy Foster said ratepayers gained benefits from all local businesses, down to corner dairies, yet were not expected to subsidise their costs. "This is yet another cost being passed on by the Government to local government," he said.

Mr Foster, a Wellington City councillor, said the Government had criticised Labour for similar behaviour forcing rates to rise.

The freight productivity report analysed responses from 26 transport providers and users which sought concessions to carry more than 33 million tonnes a year on trucks exceeding the existing maximum load of 44 tonnes.

It said they all considered that to be a constraint on efficiency, amounting to considerable evidence of "a significant hindrance to transport productivity and economic development in New Zealand".

One firm expected to save $20 million a year on short trips, and another hoped to cut 10,000km off 35,000km travelled annually by its trucks.

Others expected improved distribution systems to let them sharpen staff rosters in production plants, and one manufacturer believed it could reduce its storage tanks from seven to two.

Only one company expected to reduce its reliance on rail, against several which believed heavier trucks would make it easier to transfer freight to trains or ships at intermodal hubs.

Even so, the report said policies would be needed to ensure impacts on rail and shipping were avoided or minimised.