Uber launched a robotaxi service in Austin, Texas in March and said its driverless vehicles could work for 20 hours per day, seven days per week.
Customers there can choose whether to take a robotaxi if there is one available, with no difference in fare. Tesla is planning to launch a rival service in the same city in June.
Fully driverless cars have done millions of miles on public roads in other countries too, including China, UAE and Singapore, but whether they are more or less safe than human-driven ones is still being investigated.
Numerous studies suggest automated vehicles are less accident-prone than human drivers, based on US data.
But there have been a number of incidents involving robotaxis in the countries where they operate, ranging from road accidents to passengers being locked in.
And one service in San Francisco was cancelled after a series of malfunctions.
In May I took a ride in a car fitted out with Wayve's autonomous kit across central London. We had a human safety driver at the wheel but he did not have to use the controls once during our 30 minute journey.
The car handled every potential hazard which appeared in the busy streets including congestion, temporary traffic lights, cyclists and, at one point, a pedestrian using crutches in the middle of the road.
The Ford Mach-e was fitted with sensors and a radar, and an AI-powered system controlled the vehicle's responses in real time.
If anything it was a lot more cautious than a human driver, which made for a reassuringly uneventful trip.
