Tooting wouldn't rouse the driver as his truck rumbled down the Waikato Expressway, so members of the public took control of the situation, preventing a potential tragedy.
First, a motorist got in behind the truck and put on their hazard lights to alert other drivers to the danger and then, after the truck had crashed into a concrete barrier and was slowing, another motorist climbed into the cab and applied the handbrake.
The driver, who was initially thought to be asleep, was suffering medical issues and an ambulance was called.
Police received a call about 7am on Wednesday about a driver that had dozed off at the wheel, Waikato district road policing manager Freda Grace said.
The truck, which was loaded with a digger, was reported to be causing "massive" damage to the road barrier separating north- and south-bound lanes on the Waikato Expressway near Rangiriri.
A motorist who made the call tried to wake the truck driver by tooting, Grace said, but had no luck rousing the truck driver.
"With its speed at 20kmh the motorist got in behind the rear of the larger vehicle and activated their own hazard lights to act as a warning to following drivers," Grace said.
The clear thinking and quick actions prevented a major incident, but not before the truck crashed into a concrete barrier in a large area of road works as the lanes merged.
Grace said as the truck slowed two other motorists stopped to help and one clambered into the cab of the truck and pulled the handbrake.
"It was quickly established the truck driver wasn't asleep but was actually experiencing medical issues and an ambulance was called to the scene."
Police are investigating what lead to the crash and will find an appropriate way to recognise the members of the public who intervened.
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