WA Labor to put an end to speculation over the cost of its Metronet rail plan by submitting it to Treasury for costing.
Mr Buswell was scathing in his assessment of Labor in announcing the discrepancy.
"This highlights a massive funding black hole but more importantly an inability to add up and an inability to deliver major projects.
"These figures reinforce the view that the Labor rail plan is unaffordable, undeliverable and unrealistic.
"The critical areas of difference between the Labor plan and the cost of what the rail will actually be sit in and around the airport and sit in and around the requirement to upgrade the rail link between Bayswater and the city to carry their proposed three additional railway services
"What is clear from the PTA advice is where the rail lines hit areas of engineering complexity the Labor Party have got it wrong.
"They've got it wrong at the airport to the extent of $860 million.
"They've got it wrong in underestimating the requirement to update the rail link between Bayswater station and the City which in its current form simply won't carry the rail line capacity that they are proposing to add to it.
"To put it simply, they can't pay for it and it won't work."
However, Mr McGowan says what the PTA has costed is not Metronet.
He says the PTA has included an extra line and put in extra engineering he does not believe is neccessary.
"We know they haven't costed our proposal, our plan," he said.
"They've changed things, they've changed assumptions."
Earlier in the day McGowan would not confirm if he would submit the plans to Treasury to cost.
"Well there is always independent consultants to do it if we don't feel we have faith in a government agency," he said.
Late this afternoon Mr McGowan said he had decided to do so.
"We're going to commence discussions with Treasury next week and we will submit our plans to treasury for costing," he said.
"This will be before the election. Significantly before the election."
He has called on the Liberal party to submit the plans for its rail plans to Treasury as well.
"They need to commit to putting their rail and light rail plans into treasury for costing."
Mr Buswell says the Liberal Party will submit all of its election commitments to Treasury.