FedEx Corp. is trying out new technology to tighten spacing between freight trucks traveling on the highway as a way to increase safety, relieve traffic congestion and reduce fuel consumption.

The test of a technique called “platooning” involves three Volvo AB trucks pulling FedEx trailers separated by about 140 feet on a North Carolina toll road. The operation marks the technology’s first on-highway test in the U.S.

Fuel savings can range from 4 percent to 12 percent as drag is reduced on the two trucks following the leader. Drivers in the two trailing vehicles need only steer while braking and acceleration are done by computer.

“Most of all it’s a technology that we believe will enhance the safety of our vehicles,’’ said John Smith, chief of FedEx’s freight unit, in a telephone interview. “There’s an efficiency gain due to the fact that when you’re platooning like that, the aerodynamics change.”

The live trial relies on a Volvo-designed system to keep the vehicles in sync on maneuvers, and comes more than two years after the manufacturer platooned trucks through Europe to Rotterdam. The stretch of highway near Raleigh, North Carolina, is one of 10 locations the U.S. Department of Transportation has designated for demonstrating technologies that may lead to self-driving vehicles.

Volvo and other truck makers have been rolling out new systems such as automatic braking to avoid collisions and warnings when a truck drifts outside its lane as they work toward more autonomous vehicles.

“We know these technologies will be part of our future, but exact timing depends on many things, namely regulations, infrastructure, safety standards, and market demand,” said Per Carlsson, acting president of Volvo Trucks North America, in a statement.