Aerodynamic Drag Reduction for Heavy Vehicles

Heavy vehicles such as buses, trucks and tractor-trailer combinations experience significant pressure drag due to the inherent limitations of aerodynamic design in their construction. Fuel efficiency losses represent a sizable impact on the profitability of large and ultra-large fleet operators, leading to a growing corpus of research that supports aerodynamic drag reduction technologies to make fleets more efficient. Today, light commercial vehicles and heavy vehicles have the potential to save thousands of liters of fuel each year—a potential that can be realized by the implementation of aerodynamic components.

Designing to Save Fuel

Sports vehicles are usually the primary recipients of technological advancements in aerodynamic drag reduction, but these advancements are of immense benefit to larger, less fuel-efficient heavy vehicles. A typical trailer-truck expends up to 52 percent of the energy generated by the combustion of fuel to overcome aerodynamic drag. A study by the National Research Council of Canada has identified several key drag reduction technologies that can help trucks, buses and trailers to operate more efficiently. Research efforts by the Department of Energy have projected that a 12 percent reduction in fuel use represents an annual saving of 3.2 billion dollars. Some of the technologies explored include:

Redesign or Removal of Rearview Mirrors

The removal of drag-inducing side rearview mirrors on a tractor could save an average of nearly 940 liters of fuel each year. Alternatives to these mirrors include rear-facing cameras and video screens to replace mirrors. However, the adoption of mirrorless rearview technologies necessitates the amendment of safety regulations around the world. Despite this hurdle, smaller and more efficiently designed mirrors could be the answer to mitigating a significant percentage of pressure drag.

Fairing Design

Fairing design continues to be at the forefront of drag-reduction technologies with aerodynamic testing resulting in the use of fairing products such as side skirts for the gap between the tractor and trailer as well as for the wheels. Experiments conducted by the School of Aerospace, Mechanical and Manufacturing Engineering at RMIT University, Australia, show that front fairing alone reduces drag by 17 percent while all-body tractor and trailer fairing configurations are able to offer a reduction in aerodynamic drag of up to 26 percent. In 2012, international courier giant TNT used an innovative ‘EcoTail’—a retractable rear wing that optimized airflow at the end of the trailer, generating a saving of 1.65 liters of diesel fuel for every 100 kilometers traveled. For buses, rounding and tapering of the wind-facing surfaces as part of fairing or body design as well as advancements in underbody treatments are expected to pave the way for improved on-road efficiencies.