State Williamstown MP Wade Noonan last week met Metro chief executive Andrew Lezala to convey commuters' concerns about the use of buses between Newport and Williamstown.

As reported last week, Williamstown commuters said they were being treated like "second-class travellers" after learning their trains would be the first cancelled in the event of a "meltdown".

Metro said if there was a fleet shortage due to electrical faults caused by extreme heat, trains would be taken from the Williamstown and Alamein lines because they had the lowest patronage.

Williamstown commuters said they feared that replacing trains with buses was just the first step towards a complete shutdown, a spectre raised during the Kennett era.

Mr Noonan said Mr Lezala had been absolutely clear that the Williamstown line would stay open.

"He indicated to me quite bluntly that there is no threat to the Williamstown line," Mr Noonan said.

"There is no threat to the short, medium or long-term future of the Williamstown line."

Mr Noonan said Metro had agreed to review its back-up plans in the event of a reduced fleet caused by electrical faults in extreme temperatures.

"What they are examining now is whether instead of using buses they could run a [train] shuttle service, which would be preferable to me."

Metro spokesman Chris Whitefield said that during the recent heatwave, a strategic decision was made to conduct a trial of buses on a couple of lines to free up trains for more intense lines.

"We are now considering running three-car trains in combination with supplementary bus services in the event of extreme weather conditions that affect our fleet availability.

"We are currently working through this change with the state and will look to adopt the revised strategy should we face this situation in the near future.

"One of the faults that impacts our train fleet in extreme heat is the air-conditioner units.