Following the financial collapse of two similar tunnel projects in Sydney, Dr Jago Dodson, of Griffith University's urban research program, said it was time Brisbane City Council put a halt to plans for more tunnels until the viability of the current project was proved.

 

He claimed that environmental issues such as a planned carbon tax on fuel as well as higher oil prices were stacking up against toll road projects such as the tunnel because fewer people could afford to travel by car.

 

"They were planned when oil prices were half what they are now and so these traffic forecasts are probably out," he said.

 

He said that raised questions about whether the project could pay its way.

 

Dr Dodson said there was less risk for the city in pushing for greater public transport.

 

Shares in the project's owner, RiverCity Motorways, have halved in value in the past year, as have many similar stocks, and a report from stockbroker UBS has recommended investors sell the stock.

 

The project is a pivotal one for Lord Mayor Campbell Newman, who has refused to comment on its financial viability but said Brisbane ratepayers would not pay a cent more than the contracted $503 million.

 

Cr Newman has a plan for five tunnels to reduce traffic snarls in the city.

 

UBS said the risks included delays and blowouts in the construction, that traffic flow forecasts were not met or take longer than expected to be reached and that it was impacted by the global credit crunch.

 

Other analysts have also raised doubts about traffic forecasts, but remain far more upbeat while the company has rejected comparisons with the two failed Sydney schemes.

 

RiverCity also said its construction was ahead of schedule. There was no impact from the credit crunch because it would not be looking for more funds until 2014.

 

A spokesman said the cost of using the tunnel, which is expected to be $4.10 in today's dollars, could also be argued as good value.

 

He said a study released by NRMA in September found a free flowing toll road had the potential to save motorists money by reducing fuel consumption by up to 40 per cent compared with the stop start traffic of normal roads.