After successfully offering rides to passengers for the past couple of years in Phoenix, Arizona, Waymo has now expanded its Waymo One self-driving taxi service to the busy streets of San Francisco, California.

The San Francisco service started on Tuesday and is still in a trial phase, as the first passengers are all part of an invite-only research program known as Trusted Tester. There's also a safety driver on board for emergencies and the service is limited to a small geofenced area.

Waymo will slowly expand the service to more passengers and use their feedback to shape the service ahead of a public launch at a yet-to-be-disclosed date. In Phoenix, Waymo offered the first rides as part of trial starting in 2017 and followed with the public launch in 2020, though Covid-19 caused delays. According to the company, its Phoenix service has offered tens of thousands of rides since October 2020.

Waymo has been testing self-driving cars in San Francisco for more than 12 years, starting when the company was still a skunkworks team at parent company Google. It started offering rides to its own employees in San Francisco earlier this year.

Waymo uses Jaguar I-Pace electric crossovers for the San Francisco service. It uses Chrysler Pacifica minivans for the Phoenix service. The vehicles are controlled by Waymo's own self-driving system, known as the Waymo Driver, which is now in its fifth generation. The system is ranked at Level 4 on the SAE scale of self-driving capability as it can drive on its own, though only with restrictions. Level 5 is the ultimate goal, as this represents a system that can drive at the same level as a human.

Waymo's long-term goal is to develop a robust and reliable self-driving system capable of handling roads all over the world. The company doesn't plan to manufacture self-driving cars but rather to offer the technology as a service or directly to other firms via license. The company is developing its system for both passenger vehicles, and commercial vehicles like delivery vans and semi-trailer trucks. Waymo's self-driving delivery service will be known as Waymo Via.