An Uber self-driving car hit and killed a woman crossing a street in Arizona, police said, in the first fatality involving 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 currently going on in Arizona, Pittsburgh and Toronto.

So-called robot cars, when fully developed by companies including Uber, Alphabet Inc. and General Motors Co., are expected to drastically cut down on motor vehicle fatalities and create billion-dollar businesses.

But Monday’s accident underscored the challenges ahead for the promising technology as the cars confront real-world situations involving real people.

Lawmakers have been de­bating legislation that would speed introduction of self-driving cars.

“This tragic accident under-scores why we need to be exceptionally cautious when testing and deploying auto-nomous vehicle technologies on public roads,” said Democratic Senator Edward Markey.