Scaling Cleaner Freight Movement

Big Efficiency Gains Are Seen with Tractor Aerodynamic Devices

Aerodynamic improvement of commercial tractors has been a primary contributor to significant reductions in the fleet operating costs and reductions in harmful emissions by improving the efficiency of the use of energy to move vehicles down the road.

The per-vehicle fuel economy benefit of optimizing the aerodynamics of a tractor can be high. OEMs offer a range of tractor “models,” reflecting broad design elements that are prioritized by each of a certain segment of the trucking industry.

The importance of tractor aerodynamics is well recognized, and is a major consideration of OEMs in designing their base models and they are constantly working to improve the performance of their tractors. Each base model is aerodynamically optimized by the OEM, which will view the entire tractor as a unified system interacting with the air flows.

In addition, there are other areas of the tractor where a fleet may choose to invest in additional aerodynamic devices to further optimize their tractor. This includes things like cab extenders, roof extenders, tractor-trailer gap devices, mirrors and cameras, sunshades, headlamps, bumpers, chassis fairings, drive wheel fairings, fifth wheel location and height, wheel covers and vented mud flaps.

Tractor Aerodynamics

Adding items like tractor-trailer gap devices, chassis fairings, drive wheel fairings and wheel covers, etc., to today’s already aerodynamic tractors, allows fleets to further improve fuel efficiency.

– Laura Ricart, Chief Engineer, Vehicle Performance Integration and Aerodynamics, Navistar

Benefits

Fuel Savings
Due to lower drag
1% to 10% depending on the devices chosen

Improves Stability and Rollover
Trailer aerodynamic devices add surface area to the trailers and modify the trailer air flows. These can slightly improve rollover physics in severe crosswind conditions.

Reduces Splash and Spray
Aerodynamic device equipped trailers reduce drag by improving air flow around the vehicle, which also helps to reduce splash and spray.

Reduces Driver Fatigue
Anecdotal feedback from drivers suggests that trailers equipped with aerodynamic devices are generally less taxing and maintain their lane with less frequent steering correction by the driver.

Challenges

Adds Weight
As trailer aerodynamic devices add weight the critical trade-off between aerodynamic performance improvement and increasing tare weight will depend on the weight-sensitivity of the fleet.

Difficulty Getting Accurate Comparisons Between Devices
The different methods used to test and analyze aerodynamic devices can make it difficult to do accurate comparisons.

Variance Among Aerodynamic Manufacturer Information
Information published by the device manufacturers varies greatly in content, format, and detail.

The Need to Optimize Tractor/Trailer Ratios
The tractor-trailer ratio will indicate the trailers actual annual mileage and the return on investment from the adoption of trailer aerodynamics.

Questions About Durability and Reliability
There are no standards for structural integrity of aerodynamic devices. To survive normal daily operations and should be subject to regular driver inspection and other audits.

May Increase Tire Operating Pressure
Aerodynamic devices can modify the air flow over the brakes and tires resulting in slightly higher operating temperatures.

Common Fleet Strategies

What Fleets Are Saying

The overall perception of the savings offered by trailer aerodynamics is positive. “They are really effective devices now,” one fleet owner said.

Fleets stated that aerodynamic device construction, design, and materials have all vastly improved in the past five to seven years. They have become lighter and more robust.

Some fleets feel that drivers have become more accustomed to having aerodynamic devices on trailers and when combined with fuel economy incentive programs, actually appreciate having them.

Fleets were uniform in stating that the devices should “require no driver intervention.” One fleet owner said, “Any statement that starts with ‘All the driver has to do is…’ should be questioned.”

Fleets have been investing in trailer skirts as their first choice for aerodynamic improvements. However, now having done that they are looking at the next steps and are debating the merits of tails versus other options.

We continue to update our fleet with more fuel efficient post-2014 U.S. Environmental Protection Agency emission compliant engines, install aerodynamic devices on our tractors, and equip our trailers with trailer blades, which all lead to meaningful improvement in fuel efficiency.

— Knight Transportation

Appearance and detail of our equipment means a lot to our drivers. Drive wheel fairings don’t just save us money, but our drivers like them too.

— Brad Pinchuk, Hirschbach

Sleeper tractor aerodynamics have been finely tuned by all OEMs. Eliminating various features can add 10% to a fleet’s fuel expense.

– Chief Engineer at a Major Truck Builder

Desicion-Making Tools

NACFE has developed tools to help fleets make their decision about trailer aerodynamic devices. The Confidence Matrix, informs fleets of NACFE’s confidence in the technology being studied vs. the payback the fleet should expect to receive from the technology. An appendix of SmartWay verified trailer aerodynamic devices can be found at the end of the full Confidence Report.

Conclusions

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