Aerodynamic drag is created as air resists the movement of a vehicle. The greater the drag, the harder the vehicle engine has to work and, as a result, more fuel is consumed. At high speeds, aerodynamic drag can be the largest consumer of energy on a heavy vehicle. As a result, any improvement in aerodynamic efficiency (reduced drag) can lead to significant fuel savings.
Many new trucks are designed to incorporate aerodynamic considerations by the manufacturer and vehicles can be retrofitted with additional aerodynamic equipment.
The higher the drag coefficient of a vehicle, the higher the energy losses, resulting in greater fuel consumption. The drag coefficient tends to increase from light commercial vehicles to buses, followed by rigid trucks, and then articulated trucks. The application of aerodynamic improvement applies most beneficially to heavy vehicles operating at highway speeds. Up to half of the fuel consumption of highway trucks is attributed to overcoming aerodynamic drag.
Vehicle manufacturers have progressively addressed this opportunity by producing aerodynamically efficient prime movers. However, the integration of truck and its body/trailer offers three main areas for potential improvement: the gap between cab and trailer; the gap between trailer and road; the rear of the trailer.
Current regulatory constraints prevent fitment of some aero devices, particularly those at the rear of the trailer due to limits on rear overhang.
Skirtings aimed at reducing cab/trailer gaps may not be as applicable in the Australian road freight context, as the gap is typically shorter than that overseas.
Studies in the US have demonstrated potential fuel savings associated with various aerodynamic drag reducing measures of between 3% when considered individually, and 24% when implemented cumulatively. Aerodynamic additions to the cab are estimated to achieve a fuel economy benefit of 10–15%. Trailer modifications such as side skirtings can achieve fuel savings of over 6%.
However, the potential of these savings may not translate fully to Australia due to different vehicle configurations and regulatory limits on dimensions.
Key implementation considerations
The technology is most applicable to heavy vehicles operating at high speed (linehaul). The most obvious opportunity is to specify a new vehicle with the aero devices that the manufacturer offers, particularly because there are few providers of trailer aero kits.
Maximum fuel savings may not translate directly to Australia due to shorter truck-trailer gap, and limits on rear overhang. Any additions to a cab or trailer can also make it more prone to damage from impacts.
Some truck operators have shown a resistance to fitting fairings on the basis that they are prone to damage and extend the size of an already large trailer.
Examples of implementation
This energy efficiency report from the freight company Linfox discusses the range of measures taken to improve fuel efficiency, and the results achieved (Linfox 2009). Together with MaxiTRANS and Monash University, Linfox has investigated the benefits of aerodynamic truck and trailer technology. It was found that implementing aerodynamic technology in vehicles can reduce fuel consumption by 15%. For more information, see the Energy Efficiency Opportunities Significant Opportunities Register.
This case study provides information on the fuel efficiency benefits achieved in a heavy vehicle fleet with the use of aerodynamic cab deflectors. BOC trialled the fitting of an airflow deflector kit to the cab and assessed the subsequent fuel economy of the 41 t truck compared to the standard model. The test routes were largely long distance, both day and night, and four drivers were assessed in order to increase the reliability of the results. The trial realised a 4% reduction in fuel consumption and illustrated the significant potential benefits from cab deflectors, especially in high speed (highway) applications. The financial payback period for the kit investment was as little as five months. For more information, see Department for Transport (2011) Fuel management guide Freight Best Practice, UK Government (Opens in a new window) PDF 1.1 MB.
This Transport Canada trial program report details the fuel savings achieved in long-haul vehicles with the use of aerodynamic fittings. Trials of the freightwing trailer skirtings/fairings showed an improvement in fuel economy of 6.4%. Based on the average mileage of US fleets, the payback period would be under one year.
This case study reveals the fuel savings that may be realised with the use of aerodynamic kits on linehaul vehicles.
TNT Express in the UK undertook the fitting of a full aerodynamic kit to cab and trailer, and achieved an average fuel saving of 15.8% on linehaul vehicles. The trial found that 85% of fuel savings could be attributed to the cab roof deflector, suggesting that even operators who do not own trailers can achieve considerable fuel savings. Based on an average of 100,000 km travelled per year, a payback on their investment would be achieved in slightly over one year.
This case study demonstrates the fuel savings that may be realised with the styling of double decker trailers in an aerodynamic manner. Somerfield in the UK trialled the streamlining of its double decker trailers, with the aerodynamically styled trailer realising a fuel saving of 7% over the traditional box trailer.
For more information, see Fuel for Thought – Identifying potential energy efficiency opportunities in the Australian road and rail sectors (opens in a new window) PDF 1.5 MB.