The state government's trial of high visibility speed camera vans has been slammed by one of Australia's prominent road safety experts.

Magnetic strips will be placed on two vans in the fleet to encourage drivers to slow down in school zones.



Monash University Accident Research Centre professor Max Cameron said a covert approach would be more effective.



"The idea of being conspicuous is really in the wrong direction," he said.



"The only reason I can see for it is if you're trying to affect speeding at a particular location that may be a problem location.



"But if you're trying to affect speeding all the time then the best idea is to make sure the cameras aren't predictable or apparent and to operate them covertly."



Speed camera vans will be used in school zones in WA. Credit:Jane Dyson

Police Minister Liza Harvey said covert cameras would not be removed from "dangerous patches" of road where speeding was common."[The trial] is designed around seeing if we get a different impact from sign-written vans as to covert vans," she said.Mr Cameron said the government should not have to justify revenue raising."This proposal is part of the mindset of feeling a need to apologise for actually enforcing the law, to apologise for collecting the revenue fines," he said."But in practice, [anti-speeding measures] are very very effective if done properly and represent enormous savings to society in terms of reduced deaths and serious injuries."Ms Harvey said more magnetic strips may be used on vans if the trial proves successful."If we end up seeing that has a suppression effects on the number of infringements, maybe we'll have to consider it," she said.