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The Milford road is at present the only way in or out of Milford Sound, which lies within the Fiordland National Park.
A park-and-ride system would require people to leave their cars at a designated point and catch a bus.
Stephen Hamilton, of Horwath HTL, said unless a park-and-ride solution was brought forward, there was a risk visitors would stay away.
"I think it is essential. It's reaching a tipping point during the peak visitor season and those peak hours of the day where the visitor experience will become compromised, and no-one wants that.''
Mr Hamilton has been a tourism consultant for more than 30 years.
He was in Invercargill yesterday to speak at the New Zealand Licensing Trusts Association annual conference and at a seminar for Southland tourism operators.
The park-and-ride idea gained some traction in a 2005 report commissioned by Southland local authorities and Transit New Zealand, now the New Zealand Transport Agency (NZTA).
Back then, about 450,000 people visited Milford Sound annually, an estimated 75% of them in private vehicles.
Visitor numbers have since grown to about 600,000 annually and are predicted to continue rising.
Mr Hamilton said all stakeholders in the Southland region, including local authorities, the NZTA, operators and the Department of Conservation, needed to drive the park-and-ride solution, with central government support.
"My personal view is that the status of the Milford road needs to change. It needs to be managed so that only approved operators are [using] some parts of the road.
"I know there are lots of issues and problems with that, just as there are with tolling motorways in Auckland. But I don't think this is a tolling issue, this is an issue to do with managing visitor flows in an efficient and safe way.''
Mr Hamilton said he was in favour of the proposed Haast-Hollyford road, which would connect the West Coast with the Milford road via the Hollyford Valley.
Milford Sound was two hours' drive from Te Anau, but many tourists began their journey in Queenstown, meaning they did not arrive at Milford Sound until the middle of the day.
"It's the distance from Queenstown by road which creates this bottleneck problem. So the Haast-Hollyford road creates the opportunity to change visitor patterns and it could be of significant benefit to Haast, the West Coast, Te Anau and Southland.''
He did not know whether the highway would be built, Mr Hamilton said.
"But from a quality of visitor experience point of view, it is part of the solution. It is one of the more sensible solutions, I believe.''