<<I've done design work for trucking fleets who call these features
"worry bars." They're designed to keep the brights out of the trucker's
mirrors and to discourage tailgating.
I suspect they are legal in all 50 states, or the firm I was working for
wouldn't have been using them for 20 years.>>
Jim

If ya look at the back end of a semi tractor or the trailer you'll see
white DOT reflector's on the upper corner's of the cab and trailer.
Two red reflector's on the bottom corner's of the tractor.

The white and red stripes are along the sides, and the bottom of the
rear of trailer.

This is a DOT mandated regulation in all 50 states, as of 1995.