Police officers were justified in commencing two police pursuits which ended in crashes - one fatal, the Independent Police Conduct Authority (IPCA) has found.

However other aspects of the pursuits were found to have not been conducted in accordance with police policies.

In the first pursuit, 21-year-old Chase Glen Neary died when he failed to take a bend on his motorcycle, crashed through a railing and fell into a culvert during a short police pursuit in Picton on February 21 last year. His mother, who was the pillion passenger, suffered serious injuries.

The IPCA said the motorcycle had faulty front brakes and Mr Neary was not familiar with it, having obtained it only two days earlier.

The officer involved in the chase, which lasted only 39 seconds, saw the motorcycle speed past him from the opposite direction on Waikawa Road at 11.45pm.

"The [motorcycle's] speed at the time was such that I wholeheartedly believed that the vehicle had to be stopped," the officer said.

"I was satisfied and I still am satisfied that the speed it was doing at the time was dangerous. The position of the bike on the road led me to believe the rider was possibly drunk.

"I didn't see any other vehicles during the pursuit. When I initiated the pursuit, I positioned my vehicle more towards the centre of my lane to give myself ample opportunity if something was to arise as I come over these rises, as I round these corners, so that I am not startled by someone backing out, or a pedestrian that has emerged from their house and is walking."

While the IPCA agreed the officer was justified in launching the pursuit, the authority found he was unaware his 'Gold' driver classification had expired and as a result he was not authorised to conduct pursuits.

"The authority has found the police policy at the time was unclear, and the officer reasonably believed he was able to conduct pursuits. The policy has since been clarified," the authority's chairperson Justice Lowell Goddard said.

"The officer's speed during the pursuit, of around 120kph in a 50kph zone, whilst lawful, was nevertheless undesirable."

No recommendation was made by the authority.

In the second pursuit, two youths sustained serious injuries after the unlicensed 15-year-old driver of a stolen Nissan crashed into a tree in Fraser Park in Parnell, injuring himself and two 14-year-old passengers.

The crash investigator concluded that the main cause of the crash was excessive speed.

The police had earlier pursued the car in Newmarket, although the IPCA found at the time of the crash the police car's warning lights and sirens were no longer activated and it is not known whether the driver of the Nissan was aware of the police presence.

The authority has found the police officers were justified in commencing the pursuit after they noticed the driver of the Nissan failed to stop for a red light and nearly collided with a truck. However the officers, the dispatcher and the pursuit controller at the Northern Communications Centre did not comply with police policy for abandoning a pursuit, when the Nissan reached speeds of 100kph in a 50kph zone and ran another red light.

The authority has recommended police consider whether the officers and staff concerned should be the subject of disciplinary action or training as a result.