The state government failed to submit a ''robust'' business case for independent scrutiny to justify the east-west road link, according to Australia's major projects umpire.

Infrastructure Australia has singled out the controversial $6 billion to $8 billion road as a key example of why the public are cynical about about ''big-ticket'' infrastructure announcements.

In a strongly worded submission to a Senate inquiry examining government plans to overhaul of the advisory body, Infrastructure Australia national co-ordinator Michael Deegan warns that big spending promises are being made without proper scrutiny.

''This is a particular problem during election periods where commitments are often made, although robust business cases have not been prepared, let alone independently reviewed,'' he says.

The submission directly contradicts claims by the federal and state governments that the project has been backed by a robust business case submitted to Infrastructure Australia.