TORONTO - Liberal government promises to spend $17.5 billion on public transit through 2020 can't be trusted without legislation to guarantee the plans and funding, says a report to be released Tuesday.

While there is no specific reason to believe that the MoveOntario 2020 plan won't be delivered as promised, history suggests municipalities and commuters should press the government to legislate long-term funding commitments, said Richard Soberman, the author of the report.

When the Conservative provincial government took power in 1995 it backed away from a Toronto subway expansion and something similar could happen in the future, he said.

"We had a program that lasted for 25 years of funding 75 per cent of the capital costs of transit -- and then the government changed,'' Soberman said.

"They cancelled (the subway expansion) and so there was $80 million worth of taxpayers' money that literally went into a hole in the ground.''

Because the MoveOntario 2020 plan will take more than a decade to be fully implemented, Soberman said the cost will undoubtedly rise with inflation, which could make it difficult for a future government to fund.

The report commissioned by the Residential and Civil Construction Alliance of Ontario also says the plan is based more on political considerations rather than on need or cost effectiveness.

The plan was unveiled in an election year and the McGuinty government's blueprint to launch 52 transit projects was a bad example of top-down planning, and a reversal of the typical approach, the report argues.

Ideally, professionals should be the ones to assess need, come up with ideas, and then present them to government for approval, Soberman said.

"People have to go through some justification process to prove this is the right thing to do. Well, (in this case) it's the right thing because that's what the politicians decided we should do. I sort of question that.''

The report also makes recommendations on how to properly fund transit and prioritize projects, improving labour productivity and using road tolls.

The report is being released as a variety of stakeholders make recommendations to the government through pre-budget committees.