The Victorian Opposition has accused the Government of using speed cameras to raise revenue.

Figures from the Department of Justice show one driver is fined by a camera every 25 seconds in Victoria.

More than 300,000 speeding fines were issued between April and June this year, a 21 per cent increase on the same period last year.

The Opposition's transport spokesman, Terry Mulder, says speed cameras are being placed in areas with heavy traffic.

"It starts to move into areas that the speed camera protocols said, when they started, that shouldn't be targeted and that's on high volume roads, the bottoms of hills," he said.

"There's always the question, what is the real speed camera tolerance today? Motorists don't know and the road rule that motorists don't understand is the one that frustrates them the most."

But Police Minister Bob Cameron says police decide where speed cameras are used.

He says they play a vital role in reducing Victoria's road toll.

"Since speed cameras came in in 1989 the road toll has halved, they are a very critical part of keeping the road toll down and keeping it going lower," he said.

"Police decide where speed cameras go, and it shows in the road toll where we continue to see a reduction."