The Google-owned Waymo robotaxi service on Tuesday became available to anyone in San Francisco interested in hailing a driverless ride.
Waymo has been cautiously expanding its robotaxi service, access to which had thus far been available on an invitation-only basis.
"With tens of thousands of weekly trips, our Waymo One service provides safe, sustainable, and reliable transportation to locals and visitors to the city alike," it said in a blog post.
"Now it's available to anyone."
Some 300,000 people, more than a quarter of San Francisco's population, have signed up on a Waymo waiting list since it opened, according to the company. Riders will need the company's app to use the service.
Waymo One ride-hailing is now available in San Francisco, Los Angeles, and Phoenix, with plans to "ramp up" in Austin next.
Waymo claims its safety record is "unparalleled" over more than 20 million miles (32.2 million kilometres) logged by its autonomous cars since the first rides in the Silicon Valley city of Palo Alto in 2009.
The company cited statistics contending its driverless cars drive more safely than humans do.
The top US auto safety regulator, the National Highway Traffic Safety Administration, said earlier this month that it had opened an investigation into Waymo after reports of 22 incidents with its self-driving technology.
The preliminary probe into the robotaxi company by the NHTSA's Office of Defects Investigation will cover the firm's 444 vehicles, according to documents posted on the agency's website.
The NHTSA said reported incidents included "collisions with stationary and semi-stationary objects such as gates and chains, collisions with parked vehicles, and instances in which the cars appeared to disobey traffic safety control devices."
The NHTSA opened a similar inquest into Amazon-owned Zoox after receiving two reports that the company's autonomously operated Toyota Highlanders were rear-ended after they hit the brakes too quickly.
Zoox has been testing its robotaxis in Las Vegas, Nevada, and Foster City, California.
The NHTSA has also launched probes into Ford and Tesla as it investigates the wider deployment of autonomous technology.
GM subsidiary Cruise in April said it plans to get its self-driving cars back on the road after suspending robotaxi service late last year due to safety concerns in the aftermath of an accident in San Francisco.
