Is a roller than runs the middle. First below the belt is packed, then a layer of shelves come down flush with the rollers.
When the trailers are being emptied the exterior legs/feet are up on stands, tipping the trailer back toward the opening you see here, facilitating rolling stuff out.
There’s a lot more to these parcel trailers than meets the eye, and weighs accordingly. A “flat rail” trailer, or box, is basically that, on wheels and legs. Fork and other lifts roll things in and out, think “freight” (like big honking stuff)
