The project is not a sustainable transport solution. There are various projects that could easily reduce the number of vehicles on the existing road from Te Anau to Milford Sound, such as park and ride schemes (advised by the Southland Integrated Transport Study), and coach companies offering ‘driver goes free’ tickets to car drivers who take the coach.
There is even an existing tried and tested train route parallel to the existing road route on the first leg of the journey from Queenstown towards Te Anau, up a wide, safe valley. Sadly closed years ago along most of its length, the line is partially serviced by a tourist steam train but could be restored as a public modern railway providing transport for local people between Southland and Otago, as well as part of a transport link for tourists bound for Milford.
The monorail, by comparison, is a private venture for private profit and exclusive use by a few, contrary to the principles of freedom of access to national parks.