Alphabet’s Waymo is gearing up to launch a self-driving ride-sharing service this fall, but major problems with the technology persist, interviews with people directly involved reveal. That initially may limit the capabilities of the service, expected to operate around Chandler, a suburb of Phoenix.

Among the issues: The cars can’t always make left turns. During the year and a half that Waymo’s self-driving cars have been tested on the streets of Chandler and nearby suburbs, they’ve sometimes had to stop trying to make left turns because the software wasn’t safe enough, according to a person with access to information on Waymo’s operations. That’s particularly the case when a car is turning left without a green arrow traffic signal, a common element of driving that frequently stumps humans—let alone would-be self-driving minivans.