Uber has taken its fleet of self-driving vehicles off the roads while it investigates a Friday night crash that left one of its SUVs sitting on its side.

Police in Tempe, Arizona, were called to a crash at approximately 6.25pm Friday to find that the Uber SUV had been hit when another vehicle failed to yield, according to the Tempe Police Department. No serious injuries were reported.

The accident once again raises questions about the safety of autonomous driving technology and how it will interact with other drivers on the road. There was a person behind the wheel at the time of the Friday's accident, but an Uber spokeswoman said the vehicle was in self-driving mode and that there were no backseat riders. The company's self-driving fleet has been taken off the roads in Arizona pending the investigation. The company also suspended test vehicles in Pittsburgh, where its autonomous cars also pick up passengers, and San Francisco, where it does not.

Uber has been moving aggressively to put its self-driving vehicles on the road with passengers in the backseat. As a precaution, the vehicles have a safety engineer who can take control if necessary. Others that have been developing the technology longer, including Waymo, Google's self-driving car company, have been hesitant to put ordinary people in their cars without further testing.

Many expect self-driving vehicles will enter the market through ride-sharing services, such as Uber and Lyft. Those services tend to be more popular in urban environments, where autonomous cars will be most useful, and they've already conditioned users to put their safety and trust in the hands of relative strangers.

The crash comes as Uber grapples with a wide range of crises. Among them, several Uber employees have been accused of stealing intellectual property from Waymo and using it as the basis for Uber's self-driving technology. The outcome of that legal fight could affect Uber's future significantly.

Automobile and technology companies alike are dumping billions of dollars into the technology with the idea that one day our cars will no longer need human drivers.

But that future is still far off. In the meantime, vehicles equipped with self-driving capabilities will share the road with human motorists. That will put autonomous vehicles in situations that may seem simple but are actually difficult to navigate, such as what to do when another vehicle honks its horn.

It also remains unclear to what extent self-driving cars will be regulated by federal and state governments. Last year, the Transportation Department released a policy paper outlining 15 guidelines for developers of self-driving cars. In states across the country, legislators are debating how to allow the vehicles to be tested on functioning streets without endangering passengers and other drivers.

It's a push and pull between freewheeling innovation and regulatory oversight that many new technologies endure, but the stakes may be heightened when lives are at stake. Indeed, lawmakers on Capitol Hill have already begun debate about public tolerance for injuries and deaths as a result of self-driving cars.

More than 35,000 people in the United States were killed in motor vehicle accidents in 2015, according to the National Highway Traffic Safety Administration. The majority of those are the result of human error, and technology enthusiasts believe that number will be reduced significantly as more self-driving vehicles get on the road.

Industry observers expect media coverage of and officials' response to crashes involving self-driving vehicles will shape public perception of their safety. A fatal car collision involving a Tesla Model S received widespread attention because the vehicle was in autopilot mode at the time, though a government investigation later found there were no defects in the software.

Arizona is one of a growing number of states that allow self-driving vehicles to be tested on public roads. Its permitting requirements are also more lenient than in neighbouring California, which previously barred Uber from its roads for failing to obtain the proper permits.

Washington Post