MIT scientists have analysed truck platooning and found out how large savings in fuel can be achieved using simple solutions.
In the coming years the workplace of truckers will change considerably. Trucks travelling on the motorway in a digital convoy – a so-called platoon – will change processes in the logistics business. Platooning makes a considerable contribution towards saving energy. The Massachusetts Institute of Technology (MIT) has now shown in a study how this works. The scientists examined how the advantages of platooning can be best used in comparison to conventional transport solutions. In doing so, they first concerned themselves with flocks of birds or racing car drivers. Both reduce aerodynamic drag using a tight formation to save energy.
In their study, the scientists looked for possibilities to implement platoons such that the vehicles save energy whilst delays and waiting times are avoided wherever possible. At the end of December 2016 they presented their results at the international workshop "On the Algorithmic Foundation of Robotics" in San Francisco. In their analysis they show that relatively uncomplicated schedules for autonomous vehicle fleets are sufficient to minimise fuel costs and delays. The results can be applied to conventional long-distance transportation and even ride-sharing services.
Truck platooning and flocking birds are similar challenges from a systems point of view.
"Ride-sharing and truck platooning, and even flocking birds and formation flight are similar challenges from a systems point of view," MIT professor Sertac Karaman explains. "People who study these systems only look at efficiency metrics like delay and throughput. We look at those same metrics in conjunction with sustainability issues such as costs, energy and environmental impact. This line of research might really turn transportation on its head."
According to Karaman, over long distances in particular, a truck consumes the greatest part of its fuel solely to assert itself against aerodynamic drag. Scientists have found out that energy consumption can be reduced considerably when trucks drive closely, one behind the other. According to these calculations, vehicles in the middle of the platoon achieve fuel savings of up to 20 percent. The truck at the very rear of the platoon reduces consumption by 15 percent due to air currents dragging behind.
How many vehicles should a convoy have in order to travel the most efficiently?
The more vehicles that form a platoon, the greater the savings are. However, this is accompanied by one cost factor, which arises from the time required to put together a convoy.
Testing two systems
Karaman and his colleagues developed a mathematical model to determine the effects of different scheduling policies on fuel consumption. The study group examined how the arrival times and fuel consumption changed within two scheduling methods:
A "timetable policy", whereby the platoons form and start at defined times. And a flexible system, whereby the vehicles group and set off on demand when a certain number of trucks are ready to depart. Karaman is familiar with this procedure from his home country. "I grew up in Turkey, where there are two types of public transportation: normal buses that follow a fixed timetable, and vehicles where the driver will sit and wait until the bus is full before departing," Karaman explains.
In Turkey, the bus driver sets off when the bus is full
During their search for a vehicle platooning model, the scientists analysed numerous scenarios for the different policies. In doing so, they compared, for example, the effects of varying time intervals for the departure times. In the case of the "feedback policy", they compared the effects of the number of vehicles forming a platoon.
According to Karaman and his colleagues, their findings showed that the platoons put together in defined time intervals were more sustainable and resulted in greater savings than those convoys which employed variable intervals. In the case of the "feedback group", it became apparent that the platoons that delivered the best results were those that always travelled with the same number of trucks.
Five percent less fuel
However their findings also showed that the "feedback groups" were more effective than the "timetable convoys". Overall they saved five percent more fuel. "You'd think," Karaman says, "a more complicated scheme would save more energy and time, but we show in a formal proof that in the long run, it's the simpler policies that help you." Karaman advises that in future, trucks should travel on the motorways at a distance of between three and four metres from each other.
The research group also applied their simulation to autonomous ride-sharing services – specifically to a system of driverless shuttle vehicles which transports passengers between stops. Here, ticket prices and times should depend on the energy capacity of the system and the necessities of the timetable. Thus the simulations could determine the optimum number of passengers per shuttle in order to save fuel and avoid stoppages. "We believe that ultimately this thinking will allow us to build new transportation systems in which the cost of transportation will be reduced substantially," Karaman explains.
The infrastructure, for example: in this interview, Martin Zeilinger, Head of Advance Development at Daimler Trucks, explains which hurdles truck platooning must overcome.
Just how far away is platooning from practical use?
Martin Zeilinger: We have already proven ourselves in a practical test on several occasions. Most recently in 2016 with a journey from Stuttgart to Rotterdam as part of the European Truck Platooning Challenge in which we used our 3-truck platoon equipped with Highway Pilot Connect.
Are there any specific results from these practical tests?
We were able to demonstrate the fundamental function of the system without any problem. Scenarios such as other traffic users merging, forming and breaking up the platoon and braking manoeuvres involving the whole group were completed successfully under real conditions. Happily, the practical test was "fairly unspectacular" and provided the drivers with a relaxed tour thanks to Highway Pilot Connect, the system that allows semi-autonomous and electronically coupled truck driving.
Which regulatory requirements must be created for practical operation?
In our opinion it is the general regulations that represent the greatest challenge. Especially as there are no uniform specifications, either in Germany or in the EU. However, we also need pay attention to the infrastructure. In particular it is bridges in a state of disrepair, a lack of LTE coverage, poor road markings as well as heavy traffic and traffic jams that hinder the optimum use of platooning considerably. There must also be some ruling as to the defined conditions under which a driver can underrun the mandatory minimum distance between vehicles.
How great are the energy savings when platooning is used?
Test runs on a level test route with three tractor/semi-trailer combinations and a constant speed of 80 km/h resulted in a 7 percent reduction in fuel consumption on average. The reduction differs depending on each vehicle's position in the platoon: in the case of a three-truck platoon, the lead vehicle profits from a reduction of two percent, the vehicle in the middle eleven percent and the vehicle at the rear nine percent. The differences are due to the different effects aerodynamics have on the individual vehicles.
What can be done to balance out the different savings?
Here, various, very different options for distributing savings are possible. For example using corresponding calculation models for distributing savings amongst various haulage companies when trucks produced by different manufacturers form platoons in long-distance haulage. But even without this "cost-sharing", the lead vehicle also always saves an appreciable amount of fuel. However, we first need to master the regulatory challenges named above.
How large should the individual groups be?
The maximum length of the platoon is not governed by the range of the transmission signals, but by the number of vehicles. A stable connection must be guaranteed at all times. Furthermore, an "accordion effect" must be prevented. Therefore, there is no sense in coupling more than ten vehicles.
Would it make sense to put together the individual platoons according to destination and schedules?
In the long-term that would definitely make sense. The first step is, of course, for trucks equipped with the relevant technology to come together.