The Waikato Expressway and Kainui Rd overbridge near Taupiri. This section of the expressway has suffered from rutting problems.

Brand new sections of the Waikato Expressway are falling to bits and it's costing taxpayers dearly.

Engineers are still trying to figure out how to fix it permanently and in the meantime it's a potential risk to motorists, a road safety campaigner says.

Rutting has occurred at points in Te Rapa and Ngāruawāhia after the roads opened in 2012 and 2013 respectively.

KELLY HODEL/STUFF The NZTA have repaired the Te Rapa section of the Waikato Expressway three times.

Three interim rutting repairs on the Te Rapa section have cost the New Zealand Transport Agency $755,000 and no final fix has been found.

The Ngāruawāhia section has been repaired nine times with that cost covered by the contractor.

NZ TRANSPORT AGENCY Rutting on the Ngaruawahia section of the Waikato Expressway has been fixed nine times since it opened in 2013.

Clive Matthew-Wilson, the editor of the car review website dogandlemon.com, said ruts on New Zealand roads are a serious safety issue.

"Many accidents start with a loss of control. A rutted road surface affects the ability of the driver to control a vehicle."

An outspoken road safety campaigner, Matthew-Wilson said the Waikato expressway's built-in safety features should protect motorists from accidents.

NZ TRANSPORT AGENCY Rutting on the Te Rapa section of the Waikato Expressway that has cost $755,000 for an interim fix.

"Because most of this highway has median barriers and roadside fencing, ruts on the road are less of a safety issue than they would be on a small rural road.

"However, if one lane of the Waikato expressway has an obvious defect in the road surface, oncoming drivers may see the defect then veer over to avoid it, potentially causing a collision with the vehicle in the next lane."

He said that it's concerning when a relatively new road starts giving problems so early.

Matthew-Wilson believes that the incorrect road surface was applied to the Waikato expressway when it was first built.

NZTA is working closely with the contractor to determine the root cause of the rutting in Ngāruawāhia, senior manager Chris Hunt said.

"The subgrade materials below the pavement used to form the road have performed poorly and have become weaker when moisture content increases.

"This results in reduced support for the pavement layers and traffic loading makes the pavement susceptible to rutting.

"As rutting increases, the pavement and road surface start breaking up, allowing more moisture to enter the pavement causing further and rapid deterioration of the pavement," Hunt said.

The reason for the rutting at Te Rapa differed as the pavement is supported by a thick layer of rock-fill overlaying the existing soil.

"It is being confirmed through ongoing investigations that the rock layer consolidated under heavy traffic creating a loss of support for the upper pavement layers which in turn caused rutting and cracking of the road surface. Cracking of the road surface allows moisture to then penetrate and accelerate the damage to the pavement. The Transport Agency is working with experts on a long-term repair solution," Hunt said.

He said that when issues become apparent with the Te Rapa and Ngāruawāhia sections, the Transport Agency set about developing a new pavement design that could be constructed successfully in similar conditions.

This new pavement design is currently being constructed on the Longswamp, Huntly and Hamilton sections of the Waikato Expressway.

The Transport Agency has received one official complaint due to the rutting which was made by email.

"We provided the complainant with information on both the work to maintain the road surface, including rutting repairs and the process being undertaken to identify a permanent solution to the rutting issue."

NZTA said rutting has not been attributed to any accidents.