The system controls speed, braking, and spacing of the convoy. The goal is to increase safety and fuel economy.

Three big rigs barrelled up and down the 110 Freeway on Wednesday, mirroring one another in a tight pattern. Two of the Volvo big rigs bore special antennas to "talk" to one another and radar that can detect movement around them. They were accelerating and navigating without human help.

It was only a test, but the partially automated trucks provided a peek into the future of long-haul trucking. The demonstration's sponsors hope it provides a step toward completely automated transport in the years ahead.

"It's smooth, safe and efficient," said Carrie Brown, Caltrans' district director for Los Angeles and Ventura counties.

Using what's called "cooperative adaptive cruise control," the heavy trucks drive tightly together, responding to one another and their surroundings with computerized sensors, saving fuel and releasing fewer emissions. Well-plotted trips would also ease congestion, experts believe.