Car crashes on the country’s state highways are an almost daily occurrence, especially with many of us on the move over the summer break.

Getting stuck when a road is closed after a serious crash or having to snake around long detours can be annoying. But why does it take so long to clear?

But the reason the road needs to be closed for so long is because it's a crime scene, Sergeant Andy Heath from the Counties Manukau Serious Crash Unit says in a video posted online.

He says this happens after a serious crash – which is when someone has died, has the potential to die, or has suffered life-altering injuries.

There was, provisionally, 374 fatalities from 337 crashes in 2022, according to Ministry of Transport data.

This is 56 more fatalities and 52 more crashes than in 2021, but that doesn’t count the scores of crashes where people are seriously injured.

And as frustrating as the delays can be, Amdy says police have a duty to the coroner, the victims and the families of victims to fully and thoroughly investigate the crashes.

This is important so that if there is culpability, they need the “best evidence possible” to prove that in court.

He describes turning up at the scene of a serious crash like chaos. Officers are dealing with members of the public, witnesses and other emergency services who need space to do what they do best.

Sergeant Andy Heath from the Counties Manukau Serious Crash Unit talks about why the road is closed for so long after a crash. Photo: NZ Police/Supplied.

Andy says closing the road is the first thing they do to make sure the scene is safe.

“So once we’ve got the scene safe, there’s not cars flying through at high speed. Emergency services can get in, then they’ll start dealing and helping the people that are inside.

“I’ve had a scene where medical staff were dealing with a person for an hour. They were too unstable, to be, too unstable to be put in the ambulance of flown out so they dealt with them there on the ground.”

Then, the Serious Crash Unit takes over to investigate.

“We freeze the scene, control it and try and preserve all the evidence,” says Andy.

Once everything is uplifted from the scene, police make sure the road is free of lubricants, oils and spills “because what we don’t want is another crash happening”.

It 's only then, that they reopen the road.

Andy says in the meantime, detours are set up. But if the crashias in an awkward location, that is just unfortunate.

He says they try to funnel people down the nearest side roads.

“The road controlling authorities, what they want is the road open as soon as possible. They want to keep that network moving, so we have to be mindful of that.”

Andy says he understands how frustrating it is to be late because of the road closures.

“People who are delayed and they don’t know why they’re delayed is very, very frustrating.

“I always kind of have it in the back of my mind that you’re not having an any worse day than the people here in the crash.

“You’re late to your meeting, you’re late for whatever, you know. You’re not dead.”

-Rachel Moore/Stuff.