Waymo on Wednesday launched the first-ever fleet of self-driving cars for ride-share services as lawmakers debate a regulatory framework for the burgeoning technology.

Waymo, owned by Google-parent Alphabet Inc., said the service will first be offered in the Phoenix suburbs, where it was already being tested. Trained drivers will ride with passengers to supervise the initial roll-out.

"Over time, we hope to make Waymo One available to even more members of the public as we add vehicles and drive in more places. Self-driving technology is new to many, so we’re proceeding carefully with the comfort and convenience of our riders in mind," Chief Executive Officer John Krafcik wrote in a Medium post.

Backers of a long-stalled Senate measure to launch an initial oversight program for autonomous driving technology began circulating revised language for the bill, signaling a possible breakthrough with Democrats and trial attorneys that were opposed to prior versions of the legislation.