It's a road rule that caused confusion for NSW motorists - even after it was changed.
In 2018, the government brought in a new rule that required motorists to slow down to 40km/h when passing an emergency vehicle parked on the side of the road with its lights flashing.
The move was initially welcomed by paramedics but the Police Association of NSW later expressed "serious concern" about the potential for crashes caused by motorists suddenly braking at the sight of flashing lights.
It was a rule that also created concern for motorists, who would be travelling on a road and find vehicles in front suddenly slowing well before they'd spotted the emergency vehicle.
So, after the 12-month trial was completed, the rule was altered again last year, to remove the need to slow down to 40km/h on roads where the speed limit was 90km/h or more.
But some motorists don't seem aware of the change, and are continuing to slow down to 40km/h along roads like the M1 Princes Motorway and the 90km/h section of Memorial Drive.
"Motorists passing the flashing lights of a stopped tow truck, breakdown assistance or emergency vehicle in a higher speed environment need to exercise their judgment in order to slow down to a reasonable speed for the circumstances," the spokesman said.
To work out a safe speed, motorists need to consider whether the stationary vehicle is close to traffic, if there are pedestrians moving about, and the speed of vehicles around them.
On roads where the speed is 80km/h or less, drivers are still required to slow to 40km/h.
The change to the rule also expanded the types of vehicles with flashing lights covered to include stationary tow trucks and breakdown assistance vehicles.