Ever heard of truck platooning? It's happening on the Triangle Expressway.

The three white tractor-trailer trucks driving up and down the Triangle Expressway on Wednesday didn't look all that remarkable, aside from the lack of big signs or logos on their sides. Only the small radar and antennae rising from their mirrors suggested that the trucks contain the latest technology designed to assist drivers and prevent accidents.

Volvo Trucks and FedEx disclosed Wednesday that they have been testing the technology on the toll road in western Wake County since April. The federal government named the Triangle Expressway, also known as N.C. 540, one of the country's 10 "proving grounds" for autonomous vehicle technology early last year, and Volvo and FedEx are the first companies to take advantage of it.

The companies are testing an advanced form of cruise control that allows two or more trucks to communicate with each other and drive closer together in small convoys or "platoons." The first truck sets the speed, and the other trucks fall in line and lock in, going the same speed without the driver's foot on the pedal. If the driver in the first truck brakes or a car tries to cut in between the trucks, the following trucks will automatically brake, alerting the driver to take over.

Volvo calls the system "cooperative adaptive cruise control." Platooning trucks have the potential to use less fuel, because of the steady speed and reduced wind drag on the following trucks. But the bigger advantages, Volvo and FedEx officials stressed Wednesday, are safety from the warning and automatic braking features and the comfort of drivers.

"What we're saying today is this is an enhancement for the professional driver, to make their job less stressful and to give them more advanced warning to what's happening down the road," said Keith Brandis, vice president of product planning for Volvo Trucks North America, which is headquartered in Greensboro.

Volvo and FedEx announced their research under a tent set up near the Veridea Parkway overpass off N.C. 540, a wide spot in the road where there's plenty of room for the trucks to stage before and after their test runs up the highway.

John Smith, FedEx's incoming president and CEO, stressed that the company's interest in the technology is to improve the jobs of professional drivers, not replace them with machines. Brandis said truly autonomous vehicles are still a long way off, not only because the technology is not there yet but because government regulations don't allow it.

"I think everybody's interested in when are we going to see driverless trucks," he said. "What we've said is the role of the professional driver is needed for many years. North Carolina is one of the few states that even allow testing and development. Our customer has to operate in 48 states. So we've got to work state by state to get the laws changed and the approvals for us to even be able to test and develop for different conditions."

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Volvo is testing its platooning technology with trucks that pull twin 28-foot tandem trailers, like the ones used by FedEx. The delivery company, which owns some 12,000 tractor-trailer truck cabs, is interested in the potential fuel savings but also improved safety and a better driving experience for its more than 20,000 drivers in North America, said spokeswoman Jennifer Caccavo Cordeau

Cordeau said there are situations where FedEx trucks travel together, but she said it's not likely the company would begin platooning its trucks in threes just because the technology is available.

"We're looking to fit this technology into our operations, rather than fit our operations to the technology," she said.

Volvo is not the only manufacturer to develop platooning. Daimler Trucks announced in September that it had begun testing platooning trucks on public highways in Oregon, with the blessing of the Oregon Department of Transportation.

The N.C. Turnpike Authority and the N.C. Department of Transportation sought to have the Triangle Expressway be named a test site for autonomous vehicle technology. Dennis Jernigan, the Turnpike Authority's director of highway operations, says it will allow the state to learn about technology that is already showing up on the state's highways and to make changes to the expressway to ensure the technology works as intended.

Jernigan said the Turnpike Authority began talking to Volvo shortly after the Triangle Expressway was designated a test site in January 2017. Volvo did its early testing at an off-road track in South Carolina before bringing its trucks to N.C. 540 in April.

Jernigan said he hasn't heard that anyone even noticed.

"I don't know that anybody has recognized it," he said. "It's just like a normal trucking operation."

Richard Stradling: 919-829-4739, @RStradling