This chain of Volvos is being towed electronically by the truck in the lead.

Three Volvos being towed electronically by the truck at the head of the platoon.

Spanish drivers were treated to an amusing sight at the weekend - a truck electronically towing a chain of cars behind it.

What they were witnessing was the first real-world test of ''platooning'' technology, which places a vehicle at the head of a convoy, with a string of automatically driving cars trailing behind it.

Vehicles in the trial used their electronics to automatically keep a six-metre distance from the one in front while the convoy travelled for about 200 kilometres along a freeway just outside Barcelona at a steady 85km/h.

The trailing vehicles are able to speed up, slow down and turn in sequence with the leader, allowing drivers of the cars to ''spend their time doing other things while driving, like work on their laptops, read a book or sit back and enjoy a relaxed lunch'', Volvo says.

The follow-the-leader project is part of a three-year trial to see whether the technology has any benefits on crowded, rush-hour roads, where drivers are typically stuck in bumper-to-bumper traffic.

''People think that autonomous driving is science fiction, but the fact is that the technology is already here,''  Volvo-based Safe Road Trains for the Environment project manager Linda Wahlstrom says.

The project also aims to improve traffic safety, cut fuel use and - because it controls speed - cut down on the risk of increasing congestion.

The project, started in 2009 and expected to be completed this year, has already covered more than 10,000 kilometres of trials.

While this phase of the trial has focused on how the technology works on real roads rather than just the test track, the next phase is expected to look at the project's fuel-saving benefits.