The technology for self-driving trucks is advancing quickly, as engineers continue to test platforms like the Google self-driving car and Daimler's "Freightliner Inspiration" self-steering 18-wheeler prototype.

That process took another step forward in April when six convoys of paired semi-automated "smart" trucks arrived at Rotterdam harbor in the Netherlands from starting points as far away as Sweden and Germany, according to Agence France-Presse.

Like ducklings trailing after their mother, each truck "platoon" followed a route set by its human-driven lead vehicle, with the following trucks autonomously tracking the leader through a wireless data link. For purposes of the demonstration, every vehicle had a human driver monitoring its computers and sensors, said Eric Jonnaert, secretary general of the European Automobile Manufacturers' Association (ACEA).

The trucks will only start operating on a fully autonomous basis once designers address such challenges as enabling data exchange between trucks made by different manufacturers, according to ACEA. Six European manufacturers joined the exercise, supplying two vehicles each. The participating companies were DAF Trucks NV, Daimler AG, Industrial Vehicles Corp. (Iveco), Man Truck & Bus AG, Scania AB, and Volvo Group.

Proponents say self-driving trucks will someday offer advantages such as more efficient transport, a reduction in accidents triggered by human error, and easier traffic flow thanks to consistent cruising speed.