Queensland's police union dismisses covert speed cameras as "poker machines on wheels", but Premier Anna Bligh insists they are an important tool to help cut the state's road toll.

Police Union president Ian Leavers says Queensland's average weekly road toll has actually increased since covert cameras were introduced in early April.

"I fear that the Bligh government is becoming addicted to the revenue of speed cameras," he told reporters on Wednesday.

"Sure they rake in the dollars, however, the deterrent effect for speedsters is non-existent."

Mr Leavers said the road toll was falling before covert cameras were put on the roads.