Truck platoon demo reveals 15% bump in fuel economy

  • 10-May-2013 03:42 EDT
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A four-truck platoon demonstrates automated road trains in Japan.

Say that you’re driving when you round a bend to see four diesel transports motoring single-file in convoy formation. The trucks almost magically maintain 4 m (13 ft) of space between them by accelerating and braking in unison like a procession of circus elephants. And while the lead driver controls the entire caravan, the off-shift drivers to the rear sleep, read, and eat in their cabs.

Recently, a similar lineup of four large trucks circled a test track in Tsukuba City, Japan, to help prove out this kind of new truck platooning technology for real-world use. The demonstration showed that the short spacing in the caravan improved the fuel economy of the trucks by 15% or more on average.

Lower aerodynamic drag resistance results as the rear vehicles find shelter from the wind in a trailing cone of smooth air like drafting Tour de France riders. Surprisingly, it also turns out that the lead truck can benefit from less drag at its rear as the pressure wave ahead of the tailing vehicle in effect “pushes” the lead truck forward.

Also surprising is how the technology that’s needed to accomplish this latest feat is mostly off-the-shelf, or at least relatively straightforward to build. Each truck needed little more than a radar-based adaptive cruise control (ACC) found in today’s luxury autos, wireless communications with the other vehicles, and some fail-safe safety algorithms and systems to handle emergencies.

The 4-meter gap

The tests were conducted by researchers from the semi-governmental New Energy and Industrial Technology Development Organization (NEDO) working together with industrial, national lab, and academic experts. “Our target is to enable both large and small trucks to safely maintain a 4-m distance between vehicles in single file while driving 80 km/h (50 mph),” said Nobuo Iwai, Senior Researcher at NEDO’s Energy Conservation Technology Department.

“In addition, we expect this technology to contribute to safer driving,” Iwai said. That’s saying something given that drivers and everybody else on (and near) the road will have to depend on the system's fail-safe controls to ensure bulletproof operational safety since one error or mistake could rapidly turn into a catastrophic pile up.

The work is the latest result of NEDO's five-year, $47.7-million project to develop energy-saving intelligent transportation systems that began in 2008. The platooning R&D effort includes engineers from the University of Tokyo, Mitsubishi Electric Corp., NEC Corp., Denso Corp., and Nissan Motor Co.

“We think that this new technology can lead to a reduction in the amount of road space used by vehicles, which would help to reduce traffic congestion,” Iwai said.

Some transport studies indicate as much as a doubling of lane throughput capacity if trucks were fitted with automated speed and spacing technology. And many transport planners think that road train formations on dedicated truck-ways may ultimately accommodate the heavy freight volumes that are anticipated in high-density corridors between growing urban and commercial areas.

International platooning R&D

The Japanese demonstration is only the latest of several truck-platooning study projects that have been launched globally during the last few years. Two similar tests in Europe were concluded in 2012, and U.S. Federal Highway Administration researchers have studied the technology in the past.

“Our recently completed Sartre Project showed that it is possible for vehicles—trucks and cars—to automatically follow a lead vehicle controlled by a trained driver,” said Carl Johan Alquist, Traffic Product Safety Manager at Volvo Trucks in Gothenberg, Sweden. “Technically speaking, truck platooning is not that far away; it’s the other safety and functional issues that remain to be sorted out.”

The European Union-supported Safe Road Trains for the Environment project was led by Ricardo UK. Its platoon cruised at 85 km/h (53 mph) with a gap between each vehicle of 6 m (20 ft). The engineers selected that distance following track development work during which they tried out gaps varying from 5 to 15 m (16.4 to 49 ft). The study vehicles put in some 10,000 km (6215 mi) of road.

A couple years ago the Konvoy industrial/university project at RWTH Aachen University in Germany demonstrated a platoon of four heavy-duty trucks spaced at 10-m (33-ft) intervals. In the U.S., complementary research by the Partners for Advanced Transit and Highways (PATH) program of the University of California, Berkeley, in cooperation with Caltrans, put three-truck caravans on the road with spacing from 3 to 6 m (10 to 20 ft). And last year, the Scania Transport Laboratory, a research arm of Scania Trucks, in collaboration with the Swedish National Road and Transport Research Institute (VTI), tested truck platooning using various spacing distances on a 520-km (323-mi) shipping route.

Feasible, affordable, but safe?

Under the NEDO project, Iwai and his colleagues developed a suite of technologies to enable safe, successful operation that included an automated steering system, automatic vehicle-following system, and cooperative ACC that employed inter-vehicle radio communications.

The trucks were thus equipped to detect obstacles in front of them with millimeter-wave radar and infrared laser radars, recognize white lane lines with infrared laser radars, communicate with other vehicles via 5.8-GHz wireless links, and safely control the formation using redundant algorithms with fail-safe functions on printed circuit boards.

“By utilizing these technologies, we can control an entire caravan of trucks, reduce inter-vehicular distance, and drive a caravan smoothly,” Iwai said. The trucks exchanged information, such as the speed of the lead truck, every 20 ms via the inter-vehicle communications system.

“We are still in the stage in which our experimental vehicles drive around a test course only,” he explained. If trucks on the market are already equipped with pre-crash safety systems, lane-keeping assist systems, and ACC, he continued, they can be upgraded to cooperative ACC by just adding the inter-vehicle communications system. “Therefore, we think that the eventual system/product would be sufficiently affordable for truck owners.”

“Our next step is to obtain a permit and test this technology on public roads,” the NEDO manager noted. “To ensure safety and reliability of the system, we need to conduct many field demonstrations. In addition, we think it will be necessary to establish the international technical standards.”

Figuring out how to comply with the laws and regulations, and to gain public acceptability, will also be required.

Remaining roadblocks

The upcoming phase of international research will build on present knowledge to tackle the challenges of automating lane changing, merging, as well as joining and leaving the platoon. Means must be developed, for example, so that truck caravans in the right lane do not hinder merging for other motorists or present a barrier to general traffic flow. Other drivers must be made aware of the truck convoys in a timely and safe manner, and to stay out of them, so on- and off-road signs/indicators and local V2V broadcasts will be necessary.

The truck operators face special challenges. Overcoming drivers’ discomfort with operating a vehicle with a short, disconcerting gap in front while overcoming the very limited sightlines forward will be difficult. And dealing with the spray of rain water from the vehicles ahead may at times suspend in-line operations. Any success would seem to come down to building drivers’ complete faith in the technology, which is inherently problematic. Following vehicles may also be pelted constantly by small stones and debris from up ahead, which will slowly chip, abrade, and crack windshields.

And if convoys do mix cars and trucks, the latter must go only at the front to accommodate their longer stopping distance. New trucks must insert in the middle—a maneuver that requires training—whereas cars can attach more easily at the tail.

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