PITTSBURGH (AP) — On a three-lane test track along the Monongahela River, an 18-wheel tractor-trailer rounded a curve. No one was on board.

A quarter-mile ahead, the truck’s sensors spotted a trash can blocking one lane and a tire in another. In less than a second, it signaled, moved into the unobstructed lane and rumbled past the obstacles.

The self-driving semi, outfitted with 25 laser, radar and camera sensors, is owned by Pittsburgh-based Aurora Innovation. Late this year, Aurora plans to start hauling freight on Interstate 45 between the Dallas and Houston areas with 20 driverless trucks.

Within three or four years, Aurora and its competitors expect to put thousands such self-driving trucks on America’s public freeways. The goal is for the trucks, which can run nearly around the clock without any breaks, to speed the flow of goods, accelerating delivery times and perhaps lowering costs. They’ll travel short distances on secondary roads, too.

The companies say the autonomous trucks will save on fuel, too, because they don’t have to stop and will drive at more consistent speeds. Also, Aurora says its testing has shown that if a maintenance issue arises while one of its trucks is traveling on a freeway, the vehicle will automatically pull to the side of the road and remotely call for assistance.

The image of a fully loaded, 80,000-pound driverless truck weaving around cars on a super-highway at 65 mph or more may strike a note of terror. A poll conducted in January by AAA found that a decisive majority of American drivers — 66% — said they would fear riding in an autonomous vehicle.

But in less than nine months, a seven-year science experiment by Aurora will end, and driverless trucks will start carrying loads between terminals for FedEx, Uber Freight, Werner and other partners. Aurora and most of its rivals plan to start running freight routes in Texas, where snow and ice are generally rare.

For years, it seemed as though the initial venture for autonomous vehicles would be ride hailing in large cities. But General Motors’ Cruise robotaxi unit is struggling in the aftermath of a serious crash. And Alphabet’s Waymo faces opposition to expanding its autonomous ride service in California. The result is that self-driving trucks are poised to become the first computer-controlled vehicles deployed in widespread numbers on public roads.

The vehicles have drawn skepticism from safety advocates, who warn that with almost no federal regulation, it will be mainly up to the companies themselves to determine when the semis are safe enough to operate without humans on board. The critics complain that federal agencies, including the National Highway Traffic Safety Administration, take a generally passive approach to safety, typically acting only after crashes occur. And most states provide scant regulation.

But Aurora and other companies that are developing the systems argue that years of testing show that their trucks will actually be safer than human-driven ones. They note that the vehicles’ laser and radar sensors can “see” farther than human eyes can. The trucks never tire, as human drivers do. They never become distracted or impaired by alcohol or drugs.