Police in Arizona say it's unclear whether vehicle was in autonomous mode when incident happened...

Uber has suspended its trial of self-driving vehicles after one ended up on its side following a crash in Arizona.

It is unclear whether either of the engineers who were in the Volvo 4x4 car when the crash happened in Tempe was in control of the vehicle, or whether it was in autonomous mode, reports the Guardian.

Police spokeswoman Josie Montenegro said: “There was a person behind the wheel.

“It is uncertain at this time if they were controlling the vehicle at the time of the collision.”

She said that the crash took place because a motorist in another car had not yielded to the Uber car at a left turn. No-one sustained serious injury in the incident.

The ride-hailing business has been trialling self-driving vehicles in California and Pennsylvania as well as Arizona, but has suspended such activities in all three states while it investigates what went wrong.

It’s not the first time the company’s trial of self-driving vehicles has been in the news due to safety concerns.

In December, cycling campaigner Brian Wiedenmeier attended a demonstration of Uber’s autonomous vehicle in San Francisco and said he twice saw it make an “unsafe right-hook-style turn through a bike lane.”

Despite the issue being pointed out to it, Uber still pressed ahead with a trial on public roads, where another of its self-driving vehicles failed to stop at a red light.

> Uber self-driving cars making unsafe turns across cycle lanes – and firm knew before launching live trial

The company has also seen the departure of a number of executives including president Jeff Jones in the past few weeks and is also been under fire due to employment practices and business ethics.

Earlier this month, footage emerged of a Nissan car making a close pass on a cyclist in London as it was being tested in driverless mode.

> Video: Nissan driverless car in cyclist close pass

Born in Scotland, Simon moved to London aged seven and now lives in the Oxfordshire Cotswolds with his miniature schnauzer, Elodie. He fell in love with cycling one Saturday morning in 1994 while living in Italy when Milan-San Remo went past his front door. A daily cycle commuter in London back before riding to work started to boom, he's been news editor at road.cc since 2009. Handily for work, he speaks French and Italian. He doesn't get to ride his Colnago as often as he'd like, and freely admits he's much more adept at cooking than fettling with bikes.