The Western Freeway advisory in Ballarat worked once every 20 cars, while the check on the same freeway near Ballan undersold vehicles’ speeds by three kilometres an hour, News Ltd reports.

VicRoads confirmed to The Courier Victoria’s six speed checks, installed in the mid 1990s at a cost of $60,000 a unit, could occasionally fail to register a speed, citing “environmental” conditions for the blips. 

VicRoads road operations director Dean Zabrieszach said the advisories, which cost $50,000 to maintain each year were never switched off, and were calibrated at least once a year against a radar device. 

Mr Zabrieszach said the advisory could fail to get an accurate reading if a vehicle was within three seconds of the vehicle in front, or changing lanes.

“For the foreseeable future, the electronic speed advisory indicator at these locations will remain in place,” he said. 

Mr Zabrieszach said the checks were designed to provide the driver with an indication of their speed and should not be used to validate the accuracy of their speedometer.

Since 2006, the Australian Design Rules for new vehicles have required that speedometers must not display a speed that is lower than the actual speed of the vehicle. 

The reports of faulty speed advisory signs assume greater significance over the holiday period, with local police enforcing speed restrictions. 

Police are running a national Operation Crossroads until January 3, and Victorian police will have a particular focus on speeding holiday drivers. 

Last year during Operation Crossroads five people died on Victorian roads. 

Motorists caught speeding by less than 10km/h can be fined $185 and lose one demerit point.

william.vallely@fairfaxmedia.com.au