Fiat Chrysler and Google for the first time will offer rides to the public in the self-driving automobiles they are building under an expanding partnership.

The companies announced in the spring of last year that they would build 100 self-driving Chrysler Pacifica hybrids minivans. Those vehicles have been tested in Arizona, California and Michigan.

Waymo, Google's self-driving care project, said Tuesday that it will allow hundreds of people in Phoenix to take rides in the vehicles so that it can get feedback on the experience. People can apply on Waymo's website.

The company also said that it's expanding its fleet to 500 Pacifica hybrids.

Waymo — created by Google in 2009 — has given rides to the public before in its hometown of Mountain View, California. In 2015, it let a blind man ride around Austin, Texas, in one of its completely self-driving pods. The Phoenix program will be much larger in scale, and it will be the first to use the Pacifica minivans.

Others in the race to develop self-driving vehicles have been putting people in their cars since last fall. Uber has had self-driving Volvos on the road in Pittsburgh for some time. Boston startup nuTonomy is giving taxi rides to passengers in Singapore and Boston. In all cases, there is a backup driver behind the wheel.

Waymo said it wants to learn where people want to go in a self-driving vehicle, how they communicate with it and what kinds of information and controls they want.

Fiat Chrysler builds the Pacifica minivan in Windsor, Canada, just across the border from Detroit. It adds Waymo's self-driving software and hardware, including sensors and cameras, at a facility in Michigan. Fiat Chrysler's U.S. headquarters is in Auburn Hills, Michigan.

"This collaboration is helping both companies learn how to bring self-driving cars to market, and realize the safety and mobility benefits of this technology," said Waymo chief John Krafcik in a company release.

Our early riders will play an important role in shaping the way we bring self-driving technology into the world through personal cars, public transportation, ride-hailing, logistics and more. Self-driving cars have the potential to reshape each and every one of these areas, transforming our lives and our cities by making them safer, more convenient and more accessible.

Waymo has made clear that it intends to form partnerships with automakers and not build its own self-driving cars. It's also in talks with Honda Motor Co. about a potential collaboration.