An alternative plan to ease Perth's road congestion has been lampooned by the West Australian opposition, which says the Liberals have broken yet another election promise.

The $1.8 billion MAX light rail project was all but scuppered just weeks after the 2013 state election when Prime Minister Tony Abbott said the Commonwealth would not help pay for urban rail.

Transport Minister Dean Nalder now says the possibility of using rapid transit buses along the same route is being explored.

On Monday, opposition transport spokesman Ken Travers mocked the suggestion, arriving at a press conference in a small hatchback emblazoned with signs that read “MAX light rail on wheels”.

Mr Travers said the state government had wasted $28 million on planning MAX and was now entertaining an alterative that had much higher operational costs and would not be adequate for the growing city.

“The government has clearly now set about a plan to deliver a sub-par public transport system for the people of Perth, despite the promises they made,” he told reporters.

“This is the government looking for cheap options to try and be seen to be doing something in transport.”

Property Council executive director Joe Lenzo said uncertainty around Perth’s public transport future was causing serious delays for developments.

“The property industry supported the MAX light rail plan when it was first announced, but now that it is deferred the industry urgently needs a decision on the form and the route for the alternative plan,” Mr Lenzo said.

Member for Perth Alannah MacTiernan said the light rail project, instead of the contentious Roe 8 project, should go ahead.

“More than $1.6 billion is being spent to build the Perth Freight Link which includes Roe Highway extension 8,” she said.

“The federal government has stripped $500 million for rail expansion in Perth from the budget and redirected it to an expensive 5.2 kilometre extension that will go through environmentally sensitive wetlands.”