When the Western Australian Liberal government promised to build the Forrest Highway during the state election campaign of 2001, voters were told that a $136 million investment would see the bypassing of Mandurah and the saving of 20 minutes when travelling between Perth and Bunbury.

Before building began, however, the project’s estimated cost had blown out to $337 million as of May 2005, $370 million as of August 2005, $511 million in 2006 and $631 million in 2007. During construction, the price increased further to $705 million before finally coming in at $688 million –…