WA govt may change mind on light rail

The West Australian government has again changed its mind on a key election promise, with Transport Minister Dean Nalder saying he is now in favour of an underground heavy rail system for Perth's northern suburbs.

The state government had previously deferred a light rail commitment by three years before floating the alternative of a cheaper bus service, but Mr Nalder said on Tuesday an underground railway may be a better option for the city's north.

"In reality, I've been exploring all three and I can't commit one way or the other, but for the capital costs you get on light rail versus heavy rail, I do favour slightly that heavy rail option," Mr Nalder told 6PR Radio on Tuesday.

Mr Nalder said he would have a better idea of the direction the government was likely to take by the second quarter of this year.

Premier Colin Barnett said the benefits of heavy rail should be investigated.

"We've yet to make a decision and the transport minister is doing exactly what he should do and that's compare the alternatives," Mr Barnett told reporters.

"The project is still some way away but we do intend to go ahead with it."