Section 5 - How to select a trailer aerodynamic device

5.1 Trailer side skirts

Trailer side skirts provide a 4 to 7 percent fuel savings by minimizing the air flow under the trailer and around the back axle. Trailer side skirts are a set of panels that run the length of the trailer to extend it closer to the ground. In addition to the fuel savings, drivers report better tractor-trailer stability in cross-winds with the use of trailer side skirts, and they have been shown to reduce tire spray, which can cause visibility issues for other drivers. Trailer side skirts should be used for box-style trailers that travel long distances at highway speeds.

Figure 9: Trailer side skirts Figure 10: Estimated simple payback period range for trailer side skirts
Assumptions for the payback period calculation were: an average purchasing and installation cost of $2,515; 5 percent fuel savings for the standard skirt and 7 percent for the advanced one, 102 000 kilometres as the trailer distance travelled at highway speeds; and an original fuel efficiency of 41 L/100 km.
Table 4: Frequently asked questions - trailer side skirts

Question Answer
What issues should you consider when selecting a device for your vehicle?
  • Height and length strongly affect the effectiveness of the device.

  • Side skirts made of different materials have different weights (the pair of skirts can weigh between 70 and 160 kg). Because the additional weight affects your payload weight allowance, find out the weight of the aerodynamic device you are considering purchasing.

  • Some styles come as panels so that they can be adapted to a variety of trailers and so individual panels can be replaced if damaged.

How to spec?
  • Choose a device that comes as close to the ground as possible without causing clearance issues. The distance between the side skirt and the ground averages between 25 and 50 cm. The closer they come to the ground, the more effective they are at reducing aerodynamic drag.

  • For trailer side skirts that extend close to the ground, look for materials that are flexible and not easily broken, or that have lower flexible edges to avoid damage. Side skirts can be bent if drivers go over high curbs or snow banks. This can result in dents, which can interfere with the streamlining of the trailer and therefore reduce their effectiveness.

  • Select fairings that are longer, which are more effective at reducing aerodynamic drag.

  • Metallic devices may rust and non-metallic devices may degrade through exposure to the environment. To increase the lifetime of the device, inquire about protective coatings, the material's composition and the means of attachment.

How to install and maintain?
  • Correct installation of the panels is critical for optimum fuel savings. Install according to the manufacturer's specifications

  • Installation time can vary from 3 to 5 person hours.

  • Some dealers and manufacturers provide training on the installation or will install the side skirt for a fee.

  • Install the panels so that they come close to the rear axle of the trailer.

  • Regularly check that the trailer side skirts have not been damaged or accumulated snow and are securely in place.

What is the purchasing price range?
  • $1,500 to $3,000

What is the range of fuel savings?
  • At least 4 percent for standard trailer side skirts

  • At least 7 percent for advanced trailer side skirts
    (The U.S. Environmental Protection Agency's SmartWay program classifies trailer side skirts as being either a "trailer side skirt" or an "advanced trailer skirt", based on their fuel savings 6)

What is the estimated payback period range?
  • 10 to 18 months for standard trailer side skirts

  • 7 to 14 months for advanced trailer side skirts

5.2 Trailer rear fairing

A trailer rear fairing provides at least a 1 percent fuel savings by decreasing suction at the trailer base. It is a set of panels that are curved or angled to reshape the back end of the trailer to make it more streamlined. A trailer rear fairing should be used by box-style trailers that travel long distances at highway speeds.

Figure 11: Trailer rear fairing Figure 12: Estimated simple payback period for a trailer rear fairing Assumptions for the payback period calculation were: an average purchasing and installation cost of $2,065; 1 percent fuel savings, 102 000 kilometres as the trailer distance travelled at highway speeds; and an original fuel efficiency of 41 L/100 km.
Table 5: Frequently asked questions – trailer rear fairing

Question Answer
What issues should you consider when selecting a device for your vehicle?
  • Some types of trailer fairings that are allowed in the United States might not be allowed in Canada because they are longer (more than 0.61 metres or 2 feet). Some provinces and states require a permit to pull a trailer with fairings. Refer to the end of this section for more information.

  • Trailer rear fairings may increase docking and loading time.

How to spec?
  • Choose a device that allows for easy access to the trailer door.

  • Some devices self-extend only after a certain speed is reached.

  • Choose a device that is made of a rigid material that will not bend in cross-winds.

  • Because the additional weight affects your payload weight allowance, find out about the weight of the aerodynamic device you are considering purchasing.

  • Metallic devices may rust and non-metallic devices may degrade through exposure to the environment. To increase the lifetime of the device, inquire about protective coatings, material composition and means of attachment.

How to install and maintain?
  • Correct installation of the panels is critical for optimum fuel savings. Install according to the manufacturer's specifications.

  • Installation time varies from 1.5 to 2 person hours.

  • Some dealers and manufacturers provide training on the installation or will install the fairing for a fee.

  • Regularly check that the trailer rear fairing has not been damaged or accumulated snow and is securely in place.

What is the purchasing price range?
  • $1,500 to $2,500

What is the range of fuel savings?
  • At least 1 percent
    (The US Environmental Protection Agency's SmartWay program classifies trailer rear fairings as being either a "trailer boat tail" or an "advanced trailer end fairing," based on their fuel savings. Currently, the advanced trailer end fairing is not permitted for use in Canada.8)

What is the estimated payback period range?
  • 4 to 8 years

Provincial and state regulations

Some types of trailer rear fairings are allowed in the United States but not in Canada. These fairings produce higher fuel savings, but are too long for Canadian regulations.

Canada

Provinces and territories are harmonizing their weights and dimensions regulations. They have agreed to exclude aerodynamic devices installed at the rear of a trailer from its total length measurements, with some provisions (see Figure 13).

Figure 13: Length allowance for trailer rear fairing Council of Ministers Responsible for Transportation and Highway Safety, Task Force on Vehicle Weights and Dimensions Policy. April 2008. Heavy Truck Weight and Dimension Limits for Interprovincial Operations in Canada.


The goal is that trailers that have rear fairings will be allowed in every province. Until the regulations change, a permit is required to travel with a trailer rear fairing in some provinces..

It is important to note that some styles of trailer rear fairings that are on the market do not comply with Canadian regulations. Always consult with provincial/territorial authorities before purchasing.

United States

The Federal Motor Carrier Safety Administration has excluded aerodynamic devices from length and width measurements on the National Network (which includes interstate freeways, national highways and state highways).10 Provided trailers remain on the National Network, they are not subject to state size and weight regulations, which can vary from the federal regulations.

States regulate traffic on intrastate roads and the provisions that apply to rear aerodynamic devices vary from state to state, just as they do between Canadian provinces. In some states, a permit is required to travel with a truck equipped with an aerodynamic device at its rear.


5 Assumptions for the payback period calculation were: an average purchasing and installation cost of $2,515; 5 percent fuel savings for the standard skirt and 7 percent for the advanced one, 102 000 kilometres as the trailer distance travelled at highway speeds; and an original fuel efficiency of 41 L/100 km.

6 For more information, visit the U.S. Environmental Protection Agency's SmartWay program's Web site: www.epa.gov/smartway/transport/what-smartway/verified-technologies.htm.

7 Assumptions for the payback period calculation were: an average purchasing and installation cost of $2,065; 1 percent fuel savings, 102 000 kilometres as the trailer distance travelled at highway speeds; and an original fuel efficiency of 41 L/100 km.

8 For more information, visit the U.S. Environmental Protection Agency's SmartWay program's Web site: www.epa.gov/smartway/transport/what-smartway/verified-technologies.htm.

9 Council of Ministers Responsible for Transportation and Highway Safety, Task Force on Vehicle Weights and Dimensions Policy. April 2008. Heavy Truck Weight and Dimension Limits for Interprovincial Operations in Canada.

10 Federal MCSA, Part 658: Size and Weight, Route Designations – Length, Width and Weight Limitations www.fmcsa.dot.gov/rules-regulations/administration/fmcsr/fmcsrguidedetails.asp?menukey=658