The Western Australia Government has unveiled new details about its light rail plan, promising to build the network for $1.8 billion.

The Transport Minister Troy Buswell says the 22 kilometre Metro Area Express would connect Mirrabooka to the Perth CBD, extending to Nedlands and Victoria Park, and be finished by 2018.

He expects 25,000 people a day to use the northern line.

"It is a transformational investment in public transport by our Government which will give the people of Perth access to the type of public transport offerings that exist in major cities all over the world," he said.

He says the line would run through either the Murray or Hay Street Mall despite the City of Perth's objections.

The costings come a day after the Liberal Party promised to build a new airport rail link transporting domestic and international passengers to Perth Airport's front door, at a cost of just under $1.9 billion, if it wins the March election.

That rail line would have three stations, 3000 parking bays and be built by 2018.

The combined total for the light rail and airport link amounts to $3.7 billion.

The State Opposition says the Liberal Party cannot be trusted when it comes to public transport.

The shadow treasurer Ben Wyatt says the government has a poor record on public transport.

"I say to the West Australian public, remember Ellenbrook, remember Ellenbrook," he said.

"The Liberal Party just don't do rail."

Mr Wyatt says Labor's Metronet heavy rail plan would deliver a better deal for taxpayers and commuters.

Labor estimates its Metronet rail promises would cost $3.8 billion.