Screengrab from video provided by ABC-15, shows investigators at the scene of the fatal crash involving a self-driving Uber car and a pedestrian. Picture: ABC-15.com via AP

Tempe Arizona - An Uber self-driving car hit and killed a woman crossing the street in Arizona, police said on Monday, marking the first fatality caused by an autonomous vehicle and a potential blow to the technology expected to transform transportation.

The ride services company said it was suspending North American tests of its self-driving vehicles.

So-called robot cars, when fully developed by companies including Uber, Alphabet and General Motors, are expected to drastically cut down on motor vehicle fatalities and create billion-dollar businesses. But Monday's accident underscored the potential challenges ahead for the promising technology as the cars confront real-world situations involving real people.

The accident spurred immediate reaction from US lawmakers who have been debating whether to pass legislation that would speed introduction of self-driving cars into the United States.

Democratic Senator Edward Markey of Massachusetts, a member of the transportation committee said: "This tragic accident underscores why we need to be exceptionally cautious when testing and deploying autonomous vehicle technologies on public roads."

Autonomous mode

The Uber vehicle was in autonomous mode with an operator behind the wheel at the time of the crash, about 10pm on Sunday in Tempe, a suburb about 18km east of Phoenix.

"The vehicle was traveling northbound," police said, "when a female walking outside of the crosswalk crossed the road from west to east when she was struck by the Uber vehicle."

The victim, identifyied as Elaine Herzberg, 49, later died from her injuries in a hospital, police said. Further details on the accident were not immediately available.

Local television footage of the scene showed a crumpled bike and a Volvo XC90 SUV with a smashed-in front. Uber has been using special versions of Volvo's SUV for its testing, but a Volvo spokesman said the autonomous technology used in the vehicle at the time of the accident was not made by Volvo.

The US National Highway Traffic Safety Administration and National Transportation Safety Board said they were sending teams to investigate the crash. NHTSA also said it was in contact with Volvo. Canada's transportation ministry in Ontario, where Uber conducts testing, also said it was reviewing the accident.

Wild West

Uber and Waymo on Friday urged Congress to pass sweeping legislation to speed the introduction of self-driving cars into the United States. Some congressional Democrats have blocked the legislation over safety concerns, and Monday's fatality could hamper the quick passage of the bill, congressional aides said Monday.

Safety advocates called for a national moratorium on all robot car testing on public roads.

Advocacy group Consumer Watchdog said: "Arizona has been the wild west of robot car testing with virtually no regulations in place. That's why Uber and Waymo test there. When there's no sheriff in town, people get killed.”

Arizona has opened its arms to companies testing self-driving vehicles as a means to economic growth and jobs. Governor Doug Ducey signed an executive order in 2015 allowing for the testing of such vehicles on Arizona streets and reached out to Uber a year later, after California regulators cracked down on the company over its failure to obtain testing permits.

Self-driving cars being tested routinely get into fender-benders with other vehicles. Last week, a self-driving Uber crashed with another vehicle in Pittsburgh, fortunately without injuries.

in 2017 Uber temporarily grounded its self-driving cars for a few days following a crash with another car in Tempe. The company has been the subject of a number of complaints about its autonomous vehicles, but the company has said the cars were being driven by a human driver at the time of the incidents.

Essential to Uber's success

Uber has said its ability to build autonomous cars is essential to its success in the rapidly changing transportation industry. The company envisions a network of autonomous cars that would be summoned through the Uber app that would supplement - and eventually replace - human-driven cars.

Uber had logged 3.2 million self-driving kilometres by December 2017; it has more than 100 autonomous cars testing on the roads of the greater Phoenix area, the company's prime testing ground due to the state's loose regulations and hospitable weather. Rain, snow and ice are particularly challenging for autonomous cars. The company also tests in Pittsburgh and Toronto.

Concerns over the safety of autonomous vehicles flared after a July 2016 fatality involving a Tesla Model S. The car involved in that accident featured a partially autonomous system that required human supervision. Uber's vehicle, on the other hand, is considered a full self-driving vehicle where a human is not needed at the wheel.

Safety regulators later determined Tesla was not at fault.