Auckland employers say that traffic flows will grind to a halt before any major changes to the city's public transport system are agreed on.
The Employers and Manufacturers Association (EMA) says that a proposed rail project has been delayed too long.
EMA chief executive Kim Campbell says the rail project has taken too long to get underway because it has been delayed by futile reports on what transport options are best suited to Auckland.
A draft report by the Auckland Council and its transport agency says any alternatives to the proposed downtown rail tunnel, such as adding more bus services onto existing roads, will clog the roads further.
The leaked report says alternatives to a proposed downtown railway tunnel in Auckland will be less effective and lead to increasing congestion.
The forecasts are in the draft version of a study due for release in several weeks by Auckland Council and its transport agency.
Radio New Zealand News understands the report says bus networks on existing roads will be full within a decade and a bus tunnel would deliver fewer benefits for almost the same $2.4 billion price as the rail project.
The Government last year told the council to look at alternatives to a proposed central rail link, which would provide a loop around the inner city.
The draft report is being considered by the Government.