Waymo will be adding 500 more Chrysler Pacifica plug-in hybrid minivans to its self-driving test fleet.

Fiat Chrysler Automobiles is adding to its working relationship with Alphabet’s Waymo self-driving car unit after having provided 100 Pacifica Hybrids to the project late last year.

Waymo has worked closely with FCA engineers at the automaker’s Michigan facility to add Waymo’s self-driving technology. The retrofit has focused on changes to the plug-in minivan’s electrical system, powertrain, and chassis.

FCA will begin production of the Pacifica Hybrids next month. They’ll be equipped with self-driving technology once delivered.

“The collaboration between FCA and Waymo has been advantageous for both companies as we continue to work together to fully understand the steps needed to bring self-driving vehicles to market,” said Sergio Marchionne, CEO of FCA. “The addition of 500 Chrysler Pacifica Hybrid minivans is a further acknowledgment of the hard work put forth by both engineering teams.”

Working together in the collaboration has been helping both company realize the safety and mobility benefits of the technology, said Waymo CEO John Krafcik.

Self-driving Pacifica Hybrids are being used in test markets around the country. One of these locations, Phoenix, is starting a pilot program making these rides available to the public for the first time.

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The two companies are also exploring the possibility of working together on a ridesharing program using self-driving Pacifica Hybrids. According to sources, the service may begin at the end of this year.

Waymo will be using over 100 of the Pacifica Hybrids that the two companies agreed to jointly develop. The self-driving vehicle test project had been set to involve plug-in hybrid versions of the minivan.

Ride-hailing company Uber has taken a similar position with Volvo to test out self-driving vehicle rides with the public. Last year, the two companies agreed to upfit 100 Volvo XC90 plug-in hybrids with self-driving technology for test rides in Pittsburgh.

The Detroit News