what is this?

[HydroJim]

On my way from Cleveland to Columbus for a congressional nomination interview I witnessed two trucks with these. I've never seen them in my life or I just failed to notice them. I know sideskirts are used extensively for aerodynamics but this appeared to be made of plastic and it looked to be pushing the air under the rear axle. Or I'm crazy and it's not related to aerodynamics at all....

Let me know

[mallrat]

It's an alternative to sideskirts under the trailer, to direct air around the undercarriage. Still allows air to hit the tires, some feel this is important for cooling the brakes and tires.

[mallrat]

SmartTruck

I've got no experience with them or connection to them, I just found a link. Do with it what you will.