The Transport Minister has attacked the Opposition's railway costings, accusing Labor of significantly underestimating the price of its promises.
Troy Buswell asked Treasury and the Public Transport Authority to cost the Opposition's pledge to build a rail line to the airport.
Labor says it will cost $731 million but Mr Buswell says the true cost would be closer to $1.6 billion.
"You cannot go to the electors of WA and promise to build infrastructure and not fund it properly," he said.
"This is what happens when by their own admission the Labor party add up or develop these figures on the back of an envelope in Ken Travers' office.
"When you get it wrong you can embarrass yourself incredibly.
"The challenge for the Labor Party is to justify their costing and explain how they're going to make up an $860 million dollar shortfall in this railway line."