Drugs, alcohol and fatigue are being listed as top causes of serious or fatal crashes on a stretch of Waikato highway that has been dubbed dangerous.

Waka Kotahi NZ Transport data shows these were the main factors for causing death or serious injury on State Highway 1 between Cambridge and Piarere between 2017 and the end of 2021.

The section of highway has been called a 'death trap” and three people have died on it this year, and another six were seriously injured.

The same issues could apply to any driver on any NZ road, says driver behaviour specialist Professor Samuel Charlton, and this is 'a section of road that is not forgiving”.

Waka Kotahi is proposing a 16km four-lane expressway from the southern end of the Cambridge section to the intersection of SH29/1 at Piarere – which would replace the troubled section - but not until after 2027.

In the meantime, the agency was implementing safety measures, including a temporary speed reduction.

Charlton, a psychology professor at the University of Waikato, says this is wise because the road is unforgiving and is frequented by high volumes of traffic.

'It's not a very nice road. You have an awful lot of traffic on that road. It's just reached the limits of what it can handle.”

The driver of a van died on the highway after colliding with a truck and trailer unit on October 5. Photo: Tom Lee/Stuff.

AA Waikato District chairman Bill McMaster agrees the road is not up to standard for the volume of traffic that now uses it.

It's the number one highway in the country and is also a crucial route for heavy freight, he says.

But the surface of the road is not cut out for the large volumes of traffic and heavy vehicle movement.

'That's why I think ultimately the four-laning is so important,” says McMaster.

It took an adjustment after travelling from Auckland on the four-lane expressway, where a large part is 110kmh, and then suddenly moving back to an older road, he says.

McMaster says AA has been advocating for the expressway to be extended to Piarere, because that is where traffic volumes split.

'We are aware that funding is tightly constrained at the moment, but we believe the case for that expressway is high priority.”

The organisation supports the Waka Kotahi's installation of safety measures in the meantime, but McMaster says that is only temporary.

Flexible barriers on the Waikato Expressway, for example, are saving lives, he says.

Data shows the number of people hitting those wire barriers have increased six-fold.

The barriers separated road users from oncoming traffic and objects on the side of the road, like trees.

'If a driver loses control the wire absorbs the impact and slows the vehicle. There's no doubt they save lives,” McMaster says.

The number of strikes on the Cambridge section is the highest across the expressway, with 91 people hitting the barrier there last year.

This is higher than 2020 where 65 people hit the wire barrier, with only 44 strikes in 2019.

There were 346 probable strikes across the Waikato Expressway between 2018 and 2021.

'That is nearly 350 times that a vehicle could have ended up colliding with something on the side of the road or going head-on into an oncoming vehicle.

A car and ambulance collided on the notorious stretch of highway on September 15. Photo: Christel Yardley/Stuff.

'If the barriers weren't there, those are the types of crashes likely to have horrific consequences.”

Driver behaviour contributed to the crashes, with lots of crashes coming down to speed, inattention, and fatigue, or things like dangerous overtaking, he says.

But he says since the Waikato Expressway opened north of Hamilton, there has been a massive reduction in crashes, which proves its extension will be effective.

The victim of the latest serious crash on the notorious stretch of highway, on November 18, has been in a critical condition in the Intensive Care Unit at Waikato Hospital but is now stable in a ward.

There has been six deaths and 26 people seriously injured in the five years between 2017 and the end of 2021.

The latest fatal crash was just before 5am on October 5. The driver of a van died after colliding with a truck and trailer unit, which left the truck driver in a serious condition.

It was the same area that claimed the lives of Rotorua ambulance officer Susan Cutler and Auckland man Deon Hadley when an Audi and ambulance crashed in the early hours of September 15.

Other factors which Waka Kotahi lists as causing crashes on the highway are poor handling, inappropriate speed, incorrect lanes or position, failing to give way or stop, poor judgement, poor observation, road factors, vehicle factors and overtaking.

Road safety expert Robert Isler says there is no such thing as a dangerous road – it is drivers that make a road safe or dangerous.

But he had not researched the specifics of that particular stretch of highway, and why drugs and alcohol and positioning could be an issue there.

It's unassuming piece of highway with a few sweeping corners, and Isler says this often causes drivers to take more risks.

'Positioning errors are often caused by lack of concentration or distraction. An easy, five-star road often tempts drivers to engage in distracting activities.”

He says being 'well” is the best protection against unsafe driving, and that positive emotions improved situational awareness which was crucial for hazard perception.

'Alcohol and drugs are used by drivers as personal coping strategies addressing underlying issues - which are often the real cause of unsafe driving.”

-Rachel Moore/Stuff.