A truck rolled onto its side on the Otaihanga roundabout north of Paraparaumu in April 2015.

A retired engineer says the Otaihanga roundabout is the worst he has seen on a state highway anywhere in New Zealand.

Laurie Petherick, who lives in Waikanae, worked as a civil and structural engineer, including road and bridge building, for about 40 years.

Five trucks have rolled or crashed at the Otaihanga roundabout since it opened in 2014, however the NZ Transport Agency said it met design standards and independent safety audits had not raised concerns with its camber.

Petherick said the roundabout has faults which make it difficult for truck drivers to navigate.

"No excuse blaming truck drivers for not knowing how to drive is going to win friends with me."

Petherick said there were three main design problems with the roundabout - the first being Otaihanga Rd was not levelled with the rest of the roundabout, creating a slope.

He said the roundabout's northern exit is also flawed, as drivers turn through about 230 degrees before exiting, as opposed to the recommended 180.

He did not understand why the roundabout's radius was so tight, when a sand dune, which was moved north during construction, was the only obstruction.

Petherick has suggested realigning the roundabout's northern exit to reduce the turning angle closer to 180 degrees.

"When the truck feels like it's starting to roll over it allows you to run out. It can take away the centrifugal forces."

He said the expressway's completion will help mitigate the issue regardless of any realignments.

"There shouldn't be any trucks on the road so it shouldn't be a problem."

He said he has been in contact with NZTA, and is satisfied they are considering addressing safety issues at the roundabout.

NZTA regional performance manager Mark Owen said signs are likely to be installed, reminding motorists to slow down heading into the roundabout, and a driver behaviour review is underway.

He said while the amount of truck rollovers was concerning, the roundabout had reduced the risk of severe or fatal crashes.

Between 2005 and mid-2013, when construction on the roundabout began, Owen said there were five serious injury crashes, and there had been none since.

He said four independent safety audits had not raised concerns about the roundabout's camber, and it met NZTA and trans-Tasman guidelines.