Further doubts have emerged about the economic case for the east-west link, with the Napthine government's secret business case revealing the benefits to Victoria could be overshadowed by the cost of building and operating the road.

The state government's own estimates show Victoria could recoup a loss-making 80¢ for every $1 spent on the project if so-called ''wider economic benefits'' are excluded from the analysis.

Ron Tandberg

Although the government has long said that the benefits of the $6 billion-to-$8 billion tunnel far outweigh the costs, it has refused to provide details, insisting the project will produce a return of $1.40 for every $1 spent.

But The Age can reveal this represents a best-case scenario, relying heavily on a controversial branch of analysis known as ''agglomeration economics'', which holds that increased urban density linked to transport projects adds to business productivity.