Look closely at the image. This is a very accurate depiction of the airflow behavior surrounding a moving trailer without Airtabs™ as viewed from above. Notice how large vertical eddys of air (like small tornadoes) alternately form and “shed” making room for another to form on the opposite side.
Although not visible here, there is an additional eddy that rolls off the top of the trailer as well. These eddys tumble into the partial vacuum formed by the moving vehicle.
A lack of trailer streamlining causes a partial vacuum to form at the rear of the trailer at highway speeds. This causes turbulent air in the form of large vertical eddies to tumble into the partial vacuum and the large alternating eddies cause the trailer to sway. Disturbances from passing vehicles or obstacles tend to amplify these eddies and increase the trailer’s tendency to sway, increasing driver work load and fatigue, increasing drag and lowering fuel economy. Streamlining the trailer by tapering would be the best solution but is not practical due to a necessary reduction in trailer capacity and massive changes to docking and loading facilities.
Other functional after-market devices that will reduce drag at the rear of trailers do exist. These are usually devices that physically alter the trailer rear by using inflatable sails, fiberglass boat tails or rigid metal panels that extend to taper the trailer rear. However, these devices can be cumbersome, expensive, heavy and prone to collision damage. These devices can also interfere with loading operations.