United Parcel Service Inc. is adding Waymo, the autonomous vehicle unit owned by Google parent Alphabet Inc., as a second partner to test its driverless system on large trucks the courier uses to move packages between its sorting hubs.

UPS, which tested autonomous delivery vans with Waymo in the Phoenix area beginning last year, will expand that partnership to include big rigs, Waymo said in a statement. The courier first began testing autonomous technology on 18 wheelers with TuSimple in Arizona after taking an equity stake in the startup in 2019. The Waymo tests will be done for UPS’s North American Air Freight unit for delivery routes between Dallas and Houston.

Waymo expects to learn from the tests “about how autonomous driving technology can help enhance safety and efficiency,” it said in a statement, and to “understand how to refine our autonomous operations in this use case for eventual scaling.”

Waymo has said trucking and logistics is a key part of its strategy to make money from self-driving vehicles, along with ride-hailing robo-taxi services. Earlier this summer, Waymo Via, the company’s trucking division, began tests carrying freight in Texas using autonomous trucks with J.B. Hunt Transport Services Inc., the largest long-haul trucking company in the U.S. Fully autonomous trucks, if and when they are given regulatory permission to operate without a driver on board, would provide obvious cost savings to companies like UPS and help alleviate a chronic shortage of big-rig drivers.

There is still plenty of engineering to be done. In a virtual demo earlier this year, Waymo’s test trucks in Arizona were not yet ready to handle surface streets and left turns on their own. “Autonomous trucking is not going to be like a light switch that suddenly flips and all of a sudden now we have autonomous trucks on the road where previously we didn’t the day before,” said Waymo Via product manager Pablo Abad at the time.

In its statement, UPS said, “We’re interested in learning more about the technology, but it’s too early to determine exactly how the technology would fit into our business or commit to any specific plans.”