Platooning: connected trucks are saving fuels

Platooning describes the practise of linking trucks together, allowing them to safely drive in each others’ slipstreams to save fuel. The DEKRA Automobil Test Center investigates the fuel consumption with different distances.

The test track is 5.8 kilometer long. Photo: Wolfgang Grube

The test track measures 5.8 kilometer. Photo: Wolfgang Grube

The biggest questions of the future often start with the smallest of things. A roll of tape, for example. Thilo Nikolaus craftily makes a square frame from four thin strips of tape on the inside of his Mercedes Actros 1845’s windscreen. The shape reflects that of the rear of the truck 15 meters ahead of him. The 42 year old mechanic is a test driver at DEKRA Automobil Test Center in the Brandenburg town of Klettwitz. Together with his colleagues, Michael Hausdorf, Andreas Bönisch and Jörg Müller, Nikolaus is engaged in a special mission on the DEKRA Test Oval. On their roster are around 300 test drives involving numerous articulated trucks, which are to be driven behind one another at intervals of 15, 20 or 25 meters. As vehicles equipped for this digital cooperation are not yet on the market, Thilo Nikolaus uses the tape frame on the window as a tool to help maintain the intended distances between the trucks in the convoy. To use it, he simply aligns the rear of the truck in front with the square on his windscreen. If it remains in the frame, the distance is correct. As distances change between the vehicles, the rear will either grow and overspill the frame, or shrink within it. This form of convoy driving simulates ‘platooning’. The term describes a ‘platoon’ of several trucks which are digitally connected and travel along the highway closely behind one another. Vehicle spacing of between six and ten meters has been achieved by truck manufacturers in their own testing.

This method of convoy driving was first adopted at the end of the 1990s, under the scope of the EU joint project ‘Promote Chauffeur’. Since then, technology has made massive advances in highly developed, partially automated systems. The most recent evidence of this is the European Platooning Challenge in April 2016. Several goods vehicle manufacturers sent convoys to the rally in the Dutch city of Rotterdam, demonstrating the effectiveness of the so-called ‘digital tow bar’. Platooning will do more than merely aid highway safety. It should also bring about considerable fuel savings. These savings are cited as amounting to between seven and ten percent. An important precedent to this project – the semi-autonomous truck – is already on the horizon. Manufacturers presume that platooning trucks will be production-ready in between five and eight years. Thanks to the speed of new development, these claims seem – dare we say it – realistic. The question remains, however, whether adjusting the gap between vehicles can elicit further consumption savings. Does each meter closer to the vehicle in front result in additional savings at the pump? The DEKRA Automobil Test Center’s series of tests will investigate whether these assumptions hold any water, using DEKRA’s own equipment and testing circuit. As vehicles with the requisite digital coupling mechanism aren’t yet available, this test must rely on those four little strips of tape on the windscreen. This solution allows the DEKRA experts to replicate the digital coupling during convoy driving with conventional vehicles.

Testing with Tonnage

The protagonists of this field test are typical 460 HP large-cab long-distance haulage machines from Volvo, Scania, Mercedes Benz and MAN. The quartet are then mounted with four identical trailers from Schmitz Cargobull with sliding tarpaulin sides. At the core of the test equipment is the driving data recorder, which records parameters such as distance, driving time, speed, acceleration and consumption from the vehicles’ CAN bus data system. The DEKRA test drivers’ day begins with a thorough pre-departure inspection. Following this, there are several warm-up laps on the DEKRA Test Oval in order to bring the engines of the trucks up to their regular operating temperatures. After calibrating the intended distance between the conjoined trucks, they return to the track together. Four laps are performed for each vehicle configuration. The program prescribes three rounds of testing, each with different distances between the vehicles. First up is the solo driving phase, during which the drivers follow each other with a kilometer in between the vehicles. Following this, the vehicles form pairs for platooning around the circuit, the following vehicle 15 meters behind the lead vehicle. After four laps, the vehicles swap positions. The lead vehicle slows and moves to the back, with the former following vehicle now taking on the leadership. They remain in this constellation for the next lap.

This procedure is repeated twice to also test the efficiency of driving with intervals of 20 and 25 meters. Their finale for the day is performed as a quartet, testing each of the distances between vehicles. Analysis of the data predominantly focuses on the fuel consumption of each vehicle in the various phases of testing. The solo journeys provide a reference figure, which is then compared with the vehicle’s performance as second, third and fourth position in the platoon. This comparison will display any economizing effects of plaDoloreme ste ipsum Xerese perspiention rem poremquam voluptatur Xerum volorec torero tooning. The crucial question is therefore what percentage of fuel a truck can save by driving in platoon formation rather than independently. The test laps are performed under predefined conditions. The stopwatch reads four minutes and 24 seconds when the trucks pass the measuring point as they exit the south curve. This is the time that it takes to complete a lap of the 5.8 kilometer test track at 80 km/h.

“It’s a test of consistency and uniformity.”

One of the test drivers, Andreas Bönisch, describes the challenge for his team: “The test drive should be coordinated and take place without any major corrections. It’s a test of consistency and uniformity.” To make it a touch more challenging, the lead driver has an additional task – maintaining a clean line in the middle lane of the test circuit. This is especially important in the 800 meter long banked corner. The trucks must be maneuvered through the corner with carefully dosed usage of the steering wheel – as little as a single uncontrolled steering movement is enough to send the lap outside of the required reference values. The drivers in the platoon don’t get to see much of each other during their laps. On the straights, following trucks remain out of sight in the rearview mirrors, their cabs hidden behind one’s own ibrating the intended distance between the conjoined trucks, they return to the track together. Four laps are performed for each vehicle configuration.

Andreas Bönischs day begins by testing the tire pressure at the test circuit. Photo: Wolfgang GrubeAndreas Bönischs day begins by testing the tire pressure at the test circuit. Photo: Wolfgang Grube The taped square on the windscreen aids the driver in containing the correct distance. Photo: Wolfgang GrubeThe taped square on the windscreen aids the driver in containing the correct distance. Photo: Wolfgang Grube The DEKRA test drivers discuss the day's schedule. Photo: Wolfgang Grube the driving data recorder logs relevant parameters. Photo: Wolfgang Grube Breaking tests on wet roads are important, too. Photo: Wolfgang Grube

The lead driver has an additional task

The program prescribes three rounds of testing, each with different distances between the vehicles. First up is the solo driving phase, during which the drivers follow each other with a kilometer in between the vehicles. Following this, the vehicles form pairs for platooning around the circuit, the following vehicle 15 meters behind the lead vehicle. After four laps, the vehicles swap positions. The lead vehicle slows and moves to the back, with the former following vehicle now taking on the leadership. They remain in this constellation for the next lap. This procedure is repeated twice to also test the efficiency of driving with intervals of 20 and 25 meters. Their finale for the day is performed as a quartet, testing each of the distances between vehicles. Analysis of the data predominantly focuses on the fuel consumption of each vehicle in the various phases of testing. The solo journeys provide a reference figure, which is then compared with the vehicle’s performance as second, third and fourth position in the platoon. This comparison will display any economizing effects of plaDoloreme ste ipsum Xerese perspiention rem poremquam voluptatur Xerum volorec torero tooning. The crucial question is therefore what percentage of fuel a truck can save by driving in platoon formation rather than independently. The test laps are performed under predefined conditions. The stopwatch reads four minutes and 24 seconds when the trucks pass the measuring point as they exit the south curve. This is the time that it takes to complete a lap of the 5.8 kilometer test track at 80 km/h.

One of the test drivers, Andreas Bönisch, describes the challenge for his team: “The test drive should be coordinated and take place without any major corrections. It’s a test of consistency and uniformity.” To make it a touch more challenging, the lead driver has an additional task – maintaining a clean line in the middle lane of the test circuit. This is especially important in the 800 meter long banked corner. The trucks must be maneuvered through the corner with carefully dosed usage of the steering wheel – as little as a single uncontrolled steering movement is enough to send the lap outside of the required reference values. The drivers in the platoon don’t get to see much of each other during their laps. On the straights, following trucks remain out of sight in the rearview mirrors, their cabs hidden behind one’s own trailer. Only when they enter the banked corner do they gain a glimpse of their colleagues’ vehicles. Slipstreaming throws up peculiarities in another area too. Initial analyses reveal that the aerodynamics of the lead vehicle play a secondary role in the performance of the following trucks. It is the trailer that provides the slipstream. Despite this, the driving resistance of the trucks in the platoon play a role in their own consumption. Different cab designs can cause a minor pendulum effect in one direction or the other.

A test under perfect conditions

Constant as a metronome, the quartet threads into the south curve. Upon passing the measuring point, the drivers confirm completion of the current lap and start a new recording for the next one. The twelve-liter six-cylinder diesel engines grumble away, quietly and evenly. Upon the approach to the north curve, a spectacular landmark draws into view – the grandstand of the neighboring Lausitzring, behind which the rotors of a wind turbine turn languidly. Shortly afterwards, the track passes through a small wooded area. Unlike on the highway, drivers don’t have to worry about close encounters with deer or boar – the DEKRA Test Oval is entirely surrounded by fencing and regularly patrolled by a huntsman to ensure no wildlife ventures onto the track. Back to business, the consumption data for two-vehicle platoons suggest that an interval of 15 meters results in savings of between eight and twelve percent for the second vehicle. The lead vehicle profits from the cooperation – the data reveals that the configuration reduced consumption by between 0.5 and 2.5 percent. This may be due to the fact that the geometry of the platoon reduces drag on the rear of the lead vehicle’s trailer. The data for vehicle combinations at greater intervals are also exciting. It reveals that the trucks don’t necessarily have to drive bumper to-bumper to economize on fuel.

The consumption data for intervals of 20 meters between trucks point towards savings of between 8.2 and 11.8 percent, whilst the savings achieved at 25 meters also remain in the eight to 11.4 percent range. The reduction in efficiency at higher distances is therefore relatively small. An increase in distance between vehicles simultaneously provides dramatic increases in safety. “Even when digitally coupled, the distance between vehicles plays an important role,” explains Uwe Burckhardt, Chief of the DEKRA Test Oval and responsible for the platooning project. One of the questions that the DEKRA experts must answer is how platooning vehicles react to unfavorable conditions when emergency braking. A possible example of this could be that the lead vehicle brakes on dry asphalt, shortly after entering a tunnel. The following vehicles, however, are still on the wet. Even when regulated by an electronic system, a small gap between vehicles could be used up very quickly. The effects of vehicle braking performance are tested by DEKRA in the second part of the investigation. The roster calls for 160 brake tests on the ABS braking track’s variety of road surfaces. Many different situations are replicated during brake testing – braking with both laden and empty trailers, on both wet and dry surfaces, with new and old tires. This task is yet another that the test drivers will master with confidence. Driving trainer Andreas Bönisch is positively looking forward to all the action.

Uwe Burckhardt, Deputy Chief of DEKRA Automobil Test Center. Photo: Wolfgang Grube

Uwe Burckhardt, Deputy Chief of DEKRA Automobil Test Center. Photo: Wolfgang Grube

Three questions for Uwe Burckhardt

What is the underlying idea behind the series of tests on the Test Oval?

Platooning promises to offer transport companies the potential to considerably increase both safety and fuel efficiency. If a truck can save between eight and twelve percent of diesel, that’s going to be very interesting. The question was, therefore, whether we can confirm the presumed advantages of platooning, and whether there is a direct relationship between fuel consumption and the size of the gap between the vehicles in the platoon.

What are the safety implications for both driver and vehicle whilst platooning?

In good conditions, the electronic system can bring the entire platoon safely to a complete stop. In practice, however, good conditions cannot be guaranteed. Dry and wet surfaces provide different friction, a laden vehicle has a different braking distance to that of an empty one, and a good tire is better at decelerating on wet surfaces than an older one. Our braking tests have shown that these factors lead to different braking distances. This could be an argument for increasing the distances between vehicles in a platoon. Even at 20 or 25 meters, there are considerable fuel savings.

What kinks are there in the platooning concept that still need working out?

The reliability of communication between vehicles is of ultimate importance for platooning’s success. If there are issues here, the safety of the platoon can no longer be fully guaranteed. The safety of wireless connections between vehicles (C2C) and infrastructure (C2I) is being investigated by our colleagues at DEKRA AT4Wireless in Spanish Malaga. Transport regulators must also introduce rules, such as to govern the maximum permitted number of vehicles in a platoon, and how a convoy may form and disband.

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