NREL has conducted a variety of studies to assess the fuel-saving potential of truck platooning and pinpoint areas in need of future research.
Platooning reduces aerodynamic drag by grouping vehicles together and safely decreasing the distance between them via electronic coupling, which allows multiple vehicles to accelerate or brake simultaneously.
Over the years, NREL has partnered with numerous organizations to conduct several extensive track evaluation campaigns to assess the fuel-saving potential of two- and three-truck platoons. Results demonstrated a wide range of fuel savings—with the lead vehicle saving up to 10% at the closest separation distances, the middle vehicle saving up to 17%, and the trailing vehicle saving up to 13%.
Researchers also assessed the impact of speed variations, road curvature, other vehicles cutting in/out of the platoon, the use of mismatched vehicles (i.e., trucks with standard and aerodynamic trailers in the same platoon), and the presence of passenger vehicles traveling in front of the platoons.
Speed, Following Distance, and Mass Impacts
In one study, NREL conducted track evaluations of three SmartWay tractors—two platooned tractors and one control tractor at varying steady-state speeds, following distances, and gross vehicle weights. While platooning improved fuel economy at all speeds, travel at 55 mph resulted in the best overall miles per gallon. The lead truck demonstrated fuel savings up to 5.3% while the trailing truck saved up to 9.7%. NREL found that several conditions impact the savings attainable, including ambient temperature, distance between lead and trailing truck, and payload weight.
Refer to the Effect of Platooning on Fuel Consumption of Class 8 Vehicles Over a Range of Speeds, Following Distances, and Mass and the Influences on Energy Savings of Heavy Trucks Using Cooperative Adaptive Cruise Control conference papers for details.
Lateral Alignment Impacts
In another study, NREL partnered with National Research Council Canada and Auburn University to determine the impacts of vehicle alignment over a range of intervehicle spacing in two-truck platoons. Track evaluation results confirmed that energy savings generally increased in a non-linear fashion as the gap reduced. However, the impact of different following-truck lateral offsets had a measurable impact—with up to a 4% reduction in fuel savings for offsets up to 1.3 meters.
At the same time, small unintentional driver offsets during everyday driving had little impact on fuel savings. Additionally, fuel-consumption savings on straight segments of the track exceeded those on the curved segments by upwards of 6%, highlighting potential differences between track evaluation results and real-world travel. Refer to the Impact of Lateral Alignment on the Energy Savings of a Truck Platoon conference paper for details.
Mixed Traffic Impacts
Another study by NREL, National Research Council Canada, and Auburn University investigated the energy-saving impact of multiple-passenger-vehicle patterns ahead of and adjacent to the platoon, cut-in and cut-out maneuvers by other vehicles, transient traffic, and the use of mismatched platooned vehicles (i.e., van trailer mixed with flatbed trailer). While the use of different trailer types and the presence of passenger-vehicle traffic patterns had a measurable impact on platoon performance in some conditions, basic fuel-saving trends remained intact. Refer to the Impact of Mixed Traffic on the Energy Savings of a Truck Platoon conference paper for details.
While earlier track evaluation studies demonstrated substantial fuel-saving benefits, they also raised questions about the thermal impacts of platooning and the reduced savings seen at close following distances in all studies. NREL conducted a follow-on study to investigate the tradeoffs between various airflow strategies for engine cooling and the aerodynamic-enabled fuel savings of platooning. Analysis results showed significant changes in the engine and under-hood air temperatures correlate with vehicle gap distance and platoon position. Refer to the Impact to Cooling Airflow from Truck Platooning conference paper for details.
NREL conducted a temporal and geospatial analysis using 210 million miles of real-world telematics data from more than 57,000 Volvo trucks to estimate the fraction of miles traveled by class 8 trucks in the United States that are suitable to platooning. Results of this large-scale study indicate that 63% of the total miles driven occur at speeds amenable to platooning. When also considering the availability of nearby partner vehicles, this number decreases somewhat to 55.7%. Refer to the Exploring Telematics Big Data for Truck Platooning Opportunities conference paper for details.
Results of this study compliment an earlier study in which NREL tapped into the Fleet DNA repository of commercial fleet vehicle operating data to estimate the fraction of total miles driven by class 7 and class 8 freight trucks that are suitable for platooning. NREL analyzed 3 million miles of high-resolution data and found that about 65% of the total miles driven by such trucks could be driven in platoon formation—leading to a 4% reduction in total fuel consumption and significant cost savings for truck operators. Refer to the Potentials for Platooning in U.S. Highway Freight Transport report for details.
NREL analyzed the results of several independent truck platooning projects conducted by various organizations as well as the results of wind tunnel evaluations and computational fluid dynamics simulations. NREL found broad consensus among results and identified areas in need of additional research—close formation and longer-distance effects, aerodynamic packages optimized for platooning, measurement of platoon system performance in various traffic conditions, impact of vehicle lateral offsets, and characterization of the national potential for platooning based on fleet operational characteristics. Refer to the Correlations of Platooning Track Test and Wind Tunnel Data report for details.
The following documents provide more information about NREL's truck platooning evaluations.
Technical Reports and Papers
RESEARCHER IV-SYSTEMS ENGINEERINGMichael.Lammert@nrel.gov