Volvo just announced the successful conclusion of the first "road train" test on a public motorway near Barcelona. Part of the SARTRE (Safe Road Trains for the Environment) project, the train consisted of 3 Volvo cars and a truck following a lead truck. The train drove over 200 km (~125 miles) at about 85 km/hr (~53 mph) and maintained a gap of 6 m (~20 ft). The project manager was pleased to report no problems with the technology as it operated the vehicles among other road users.
The project uses wireless communications so that the vehicles in the platoon mimic the acceleration, braking, and turning of the lead vehicle using autonomous control technology developed by Ricardo. On-board ADAS adds another level of safety.
The concept of platooning allows more efficient traveling on existing roads by allowing vehicles under automated control to travel closer together so that they use less space. Further experiments are underway to measure the aerodynamic benefit to fuel consumption of the road train concept. I suspect the vehicles will have to be closer together than 6 m apart to see significant fuel economy improvement.