No human safety driver behind the wheel. No human backup waiting in the sleeper berth. No closed roads or constraints on regular traffic. This was the real deal.

On the morning of June 16, a self-driving truck operated by Starsky Robotics cruised along the Florida Turnpike at 55 mph without a human aboard, a milestone in efforts to usher in an autonomous era of transportation.

Starting at a rest stop along the turnpike in Okeechobee, Fla., the truck departed and drove for 9.4 miles under its own control, all while everyday motorists simultaneously used the same stretch of road unaware of the landmark development occurring in the adjacent lane.

Starsky had conducted prior unmanned truck tests but only on closed roads.

"It was easy for people not to notice," Stefan Seltz-Axmacher, CEO at Starsky, tells Automotive News. "It went so smoothly. At one point, we even got passed by another truck."

Amid all the hype in the autonomous industry, few companies have actually taken the step of removing safety drivers from their self-driving test vehicles. Within the trucking realm, it's believed the test is the first of its kind.

Even so, there were precautions. Lead and chase vehicles bracketed the truck as it trundled down the highway. A remote operator, known as a teleoperator, monitored the truck from afar and could have intervened should anything have gone awry.

For now, the unmanned test was a one-off event, not a permanent switch in Starsky's overall testing procedure. But Seltz-Axmacher says it represents the first step in a gradual process in which such unmanned tests will increase in frequency as the company eyes the start of unmanned commercial operations in the second half of 2020.

Starsky envisions self-driving trucks running along interstates and major highways between distribution hubs, while human drivers retain a role driving in more complicated off-highway environments. And that's how the Okechobee test concluded. A remote operator took control of the truck just before it exited the highway and piloted it through a toll plaza. The truck came to a stop on a maintenance road beyond the toll plaza, and a human test driver climbed aboard.