As Google and others ramp up their plans to develop self-driving cars, one government-funded corporation in Japan is already making headway with autonomous heavy duty trucks. In order to save fuel, the New Energy and Industrial Technology Development Organization (NEDO) has programmed a convoy of four trucks to drive just four meters (about 13 feet) apart. That cuts down on air resistance, reducing drag (and thus improving fuel efficiency) similar to drafting with a race car.

NEDO's been working on the idea for a while, demonstrating a three-car convey with each car travelling about 15 meters apart (about 50 feet) in 2010. Three years later, the organization's four-car caravan is far more efficient. Japanese broadcaster NHK reports that the plan could reduce the vehicles' fuel consumption by up to 15 percent.

The four-car caravan uses one human-driven lead truck and three computer-controlled vehicles following it. The idea of having robotic vehicles automatically and expertly trail a human leader is comparable to DARPA's robotic packmule system presently in development for the US military. But NEDO's system also allows for its trucks to drive completely autonomously, without a human guiding them:

More tests of NEDO's autonomous trucks are scheduled for later this year.

Sean Hollister contributed to this report.