Motorist climbs into runaway truck's cab

As the lanes merged into one the truck crashed into a concrete barrier. Photo / NZ Police

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A member of the public prevented a potential tragedy when the driver of a 29 tonne truck suffered a medical event on a busy expressway.

Emergency services received a call about 7am on Wednesday by a motorist concerned that the driver of a truck carrying a digger had fallen asleep behind the wheel, Waikato district road policing manager Inspector Freda Grace said.

"The truck was heading south towards Rangiriri on the Waikato Expressway section of SH1 and as the motorist spoke to the emergency call taker they described the truck travelling at low speed but causing massive damage to the barriers separating north and southbound traffic.

"The motorist had tried to wake the driver by tooting but got no response," Mrs Grace said.

While the truck continued travelling at 20km/h, the motorist got in behind the rear of the larger vehicle and activated their hazard lights to act as a warning to following drivers.

As the lanes merged into one the truck crashed into a concrete barrier. Photo / NZ Police

As the lanes merged into one the truck crashed into a concrete barrier before entering into a large area of road works, Mrs Grace said.

The collision slowed the truck down enough for a motorist to enter the cab of the truck and apply the handbrake.

As police officers arrived they realised the truck driver wasn't asleep, but experiencing medical issues and an ambulance was called to the scene.

Police were looking into the circumstances of the crash and deciding how to best recognise the actions of the members of the public who intervened, Mrs Grace said.

"We have reports of the 29 tonne Mitsubishi Shogun truck being involved in a collision near Hampton Downs and other motorists seeing it weaving across the road and damaging wire rope barriers.

"When you consider the risks posed to other motorists, let alone to the roading contractors working on the road works at Rangiriri, we could very easily have been dealing with a tragedy."

The truck driver was assessed by paramedics at the scene and is now recovering, Mrs Grace said

"In line with this police urge all road users who have known medical conditions to ensure they familiarise themselves with the symptoms and management practices to keep themselves and others safe on our roads."