Devices mounted to the back of the trailer modify the airflow as it leaves the trailing edge of the side and top surface of the trailer. The flat back of the trailer is a large contributor to aerodynamic drag. Boat tails, the most common of these devices, reduce the wake field following the trailer, which can affect air some distance from the back of the trailer.
These devices typically stow flat against the rear-swinging door of a trailer. They deploy to their on-highway open position. A self-deploy feature has been incorporated into some designs that triggers a switch to open the tail at a predetermined highway speed.
Market penetration for these devices has grown and many early adopters are increasing their purchases of these devices
1% to 10% depending on the devices chosen
This list represents some manufacturers of trailer rear devices but it has not been vetted to ensure product availability.
Each area of the trailer represents an opportunity to reduce aerodynamic drag.
Both industry and government aerodynamicists have shown that the maximum aerodynamic improvement comes from a combination of sealing the tractor/trailer gap, sealing the trailer underbody, and adding a boat tail.
As each device is added, the performance of other devices will be impacted. The airflow over each device changes the operating conditions for the other devices. The performance of a combination of devices will not simply be the additive total of each device operating alone. However the greatest aerodynamic drag reduction comes from using devices in three main areas: gap, underbody, and rear. Addressing the aerodynamics of all three points of drag should give the greatest fuel savings for the vast majority of fleets.
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.
The study team developed several tools to help fleets make their decision about trailer aerodynamic devices.
• There is significant data showing fuel savings for the various trailer aerodynamic devices. The priority for device adoption by fleets is skirts, tails, front, and then other devices.