Renewed plans to build a 160km Hollyford-Haast highway through the Fiordland National Park will not stack up environmentally or economically, Forest and Bird says.
The Westland District Council's property company says it has a "memorandum of understanding" with overseas financiers for the $220 million needed to build the road and suggests a toll of $20 per head would apply each way.
But Forest and Bird advocacy manager Kevin Hackwell said yesterday he believed there would be insufficient traffic to make the toll road viable for an investor.
"There's no way that any serious backer would actually fund such a thing. I think the numbers will never stack up."
Mr Hackwell said he had yet to see the figures but estimated it would take 200,000 cars just to provide an investor with a 5 per cent return, without allowing for the inevitably high cost of maintenance.