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A Silicon Valley startup has completed what appears to be the first commercial freight cross-country trip by an autonomous truck, which finished a 2,800-mile-run from Tulare, California to Quakertown, Pennsylvania for Land O’Lakes in under three days. The trip was smooth like butter, 40,000 pounds of it.

Plus.ai, a 3-year-old company in Cupertino, announced the milestone Tuesday. A safety driver was aboard the autonomous semi, ready to take the wheel if needed, along with a safety engineer who observed how things were going.

“We wanted to demonstrate the safety, reliability and maturity of our overall system,” said Shawn Kerrigan, co-founder and chief operating officer of the company, in an interview Monday. The company’s system uses cameras, radar and lidar — laser-based technology to help vehicles determine distance — and handled the different terrains and weather conditions such as rain and low visibility well, he said.

The truck, which traveled on interstates 15 and 70 right before Thanksgiving, had to take scheduled breaks but drove mostly autonomously. There were zero “disengagements,” or times the self-driving system had to be suspended because of a problem, Kerrigan said.

Plus.ai has been running freight every week for about a year, its COO said, but this is the first cross-country trip and partnership it has talked about publicly.

End of year is peak butter time, according to Land O’Lakes.

“To be able to address this peak demand with a fuel- and cost-effective freight transport solution will be tremendously valuable to our business,” said Yone Dewberry, the butter maker’s chief supply officer, in a statement.

How long will it be before self-driving trucks are delivering goods regularly across the nation’s highways? Kerrigan thinks it’s “a few years out.”

Dan Ives, managing director of equity research for Wedbush Securities, predicts there will be quite a few autonomous freight-delivery pilots in 2020 and 2021, with the beginning of a commercial rollout in 2022. Like other experts, he believes the trucking industry will be the first to adopt autonomous technology on a mass scale.

The timeline will depend on regulations, which vary state to state, he said.

About 10 to 15 companies nationwide are working on autonomous freight delivery, Ives said. That includes San Francisco-based self-driving truck startup Embark Trucks, which last year completed a five-day, 2,400-mile cross-country trip. But that truck carried no freight.