Country Fire Authority operations manager Bernie Fradd said that fire crews on scene at a grass fire near Beaufort recently had to maneuver a truck onto the Western Highway to shield the crews from motorists, who consistently failed to slow down.

"At our district planning committee meeting the other night a group officer from Beaufort raised the issue that cars are still flying past when they're working on roadsides," he said.

"There was a fire on the freeway about a week ago near Beaufort and they ended up putting a truck on the road to try and protect themselves.

"It's important people slow down. Our people are working within metres of cars doing up to 100 kilometres an hour and the last thing we want is some of our people to get injured."

The law stating that motorists must slow while passing slow moving or stationary emergency services vehicles has now been in affect since July 1 2017, but continues to be ignored, said Northern Grampians Highway Patrol Sergeant Shaun Allen.

"It's designed to slow vehicles passing and approaching emergency vehicles displaying a red or blue flashing light, or a magenta light," he said.

'Emergency vehicle' includes ambulance, fire crew, and police, and also applies to VicRoads vehicles.

The rule applies to vehicles on both sides of the road, except for when there is a median strip. 

If there is a median strip, vehicles on the opposite side of the emergency services vehicle do not have to slow down.

Sergeant Allen said 40 kilometres per hour was chosen because it was the maximum speed at which a person could be hit and still have a have a high chance of survival.

"It's the maximum speed at which a pedestrian is likely to survive impact," he said.

"Research has shown that if a pedestrian is struck by a vehicle travelling 30 kilometres per hour the survival rate is 95 per cent.

"This drops to 60 per cent at 50 kilometres an hour but drops to 20 per cent at 65 kilometres an hour."

Failing to slow down can earn drivers a $322 fine.

Mr Fradd said that in the case of the Country Fire Authority, the ongoing disregard for the rule put volunteer firefighters at further risk.

"Most of our crews are volunteers so we're going out there in our own time and it's critical that we look after the safety of everyone, all emergency responders," he said.

"It (100 kilometres) doesn't seem much when you're in the car but when you're standing beside it it's amazing how fast it is."

Close calls were common.

"As a firefighter, a copper or an ambo, everyone's had close calls where you just think gee, that was a bit tight," Mr Fradd said. 

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