UPS has been quietly using autonomous trucks to deliver cargo between Phoenix, Tucson, and Arizona since May. The delivery company announced that it took a minority stake today in TuSimple, a Chinese San Dieog-based autonomous long-haul trucking startup — and that it’s been testing the company’s trucks with its own cargo.

For now, though, a driver will remain behind the wheel, which state law requires for any self-driving vehicle with an on-board computer that’s in full control of its operation.
TuSimple promised UPS that its self-driving trucks will be able to reduce the costs of shipping goods by 30 percent, according to a press release.

TuSimple’s Navistar trucks feature nine cameras that allow it to see and analyze its surroundings. The startup is also backed up by tech giant Nvidia, which is developing its own autonomous driving platform.

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The news comes after Uber shut down its self-driving truck division months after one of its self-driving cars struck and killed a pedestrian in Arizona.

And in May, the U.S. Post Office announced it will ship mail across the thousand-mile stretch between Dallas and Phoenix using self-driving trucks as well.