Back around the middle of last decade, the Australian arm of US architecture and engineering giant AECOM no doubt thought it had secured a good win when it bagged a contract to provide traffic forecasts for Brisbane’s Clem Jones tunnel.

Unfortunately, those forecasts – which project operator RiverCity Motorways Group quoted in the prospectus for an initial public offering which raised $724 million in 2006 – turned out to be short by almost four-fifths by the end of the tunnel’s first year in operation. AECOM has since spent several years…