Macedon Ranges Highway Patrol Sergeant Brad Hall said members were concerned devices placed along key roads in the region to detect when an imperceptible, icy layer might have formed on the road surface weren’t being taken seriously.

“Local exposure would suggest the vast majority of motorists were ignoring black ice warning signs and not driving to the conditions,” Sergeant Hall said.

Highway patrol members from Bendigo to Kyneton have been running extra patrols in the Macedon Ranges since May 1 as part of an operation aimed at preventing serious road trauma during the cooler months.

Operation Tinsel ends on June 30.

Related: As overnight temperatures drop, the risk of black ice rises

But Sergeant Hall said concerns black ice warning signs were being ignored were longstanding, and had been raised with VicRoads.

“Black ice detectors are installed in high risk areas across the northern region to help keep all road users safe,” VicRoads northern regional director Brian Westley said.

“If you see signs warning of black ice please drive with extreme caution, even if the road appears to be clear. Slow down, brake slowly, stay a safe distance from the car in front and keep to the left lane where possible."  

VicRoads has 13 black ice detection sites on Calder Freeway bridges between Gisborne and Kyneton, and three on sections of Black Forest Drive between Macedon and Woodend. 

“Black ice is invisible and dangerous – it can form in freezing temperatures when there is heavy dew, rain or pooled water on the road,” Mr Westley said.

Black ice detection devices assess the potential of black ice forming by measuring temperature and skid resistance levels.

Conditions likely to result in black ice trigger the warning signs and, in some locations, bridge heaters.

Related: Do you know what to do if you hit black ice while driving?

It is understood black ice warning signs can also be activated remotely by the VicRoads Traffic Management Centre team, should the team become aware of black ice forming in nearby areas.

Upgrades to the ice warning signage on Black Forest Drive is underway.

VicRoads expects the works to be completed, ‘in the next couple of months’.

The Bendigo Advertiser understands the same upgrades were finished on the Calder Freeway last year.

Ice detection sites in the Macedon Ranges have been updated previously, with the 13 ice detection sites on the Calder Freeway improved in 2014 as part of a $500,000 works package with Black Forest drive sites upgraded in 2015.

VicRoads has warned black ice could still be present on different sections of road during freezing conditions, even when warning signs were not activated.

The authority urged motorists to drive to conditions, and to report any road hazards – including black ice and snow – to VicRoads on 13 11 70.