Victorian motorists reminded to read the warning signs when it comes to speed

VicRoads has defended Victoria's speed advisory signs after the Road Safety Camera Commissioner questioned their accuracy.

An audit found only one out of the six installed across the state had the same accuracy as a fixed speed camera.

The electronic signs are fixed to overhead gantries and are used to inform motorists of the speed they are travelling at.

Commissioner Gordon Lewis said the signs' accuracy needs to be improved, or the cameras removed.

RACV spokesman Dave Jones said it was import the signs tell motorists what their actual speed is.

Dean Zabrieszach, VicRoads Director of Road Operations, told 9NEWS they accept the signs have a three kilometre margin of error when compared with fixed cameras.

"Ours are purely advisory - the police devices are for enforcement purposes," Mr Zabrieszach said.

He said the speed advisory signs are calibrated up to four times a year at a cost of around $200,000.

VicRoads is set to review the use of the signs in the new year.