Smaller booze buses could be dispatched across Perth to catch drink-drivers using suburban back streets and narrower inner-city roads under a plan being considered by police.

Four large booze buses currently operate across the metropolitan area and usually need to be placed on larger roads or freeways.

Police Commissioner Karl O'Callaghan is looking for a more flexible option.

"Currently, we have very large busses and when we place them it's quite awkward, in some circumstances, to deploy them because they have to be placed where you're not obstructing traffic," he said.

"What we have been looking at is a scenario where we would buy more booze buses but smaller ones, so that they were more mobile and you could place them in different areas."

The idea is still in its concept stage.

Once police work out exactly how many smaller booze buses they want and what they will cost, they will take the plan to the Road Safety Commission to seek funding through Western Australia's Road Trauma Trust Account.

The plan would also need to be approved by Police and Road Safety Minister Liza Harvey.

Commissioner O'Callaghan said the move would at least double the number of booze buses currently available.

"That's the thinking at the moment. We haven't actually got to the purchasing stage yet but it is a potential strategy for the future," he said.

"This is information that's come back to us from our traffic area, who would like us to change the makeup of the way the booze buses run."

The new buses would also be equipped with drug-testing equipment.

Police are looking at equipment used by other Australian jurisdictions to see if they can find a faster and less expensive mobile drug-testing system.