Abstract: The present invention relates to an aerodynamic drag reducing system for land vehicles, in particular semi-tractor trailers. The drag reducing system includes a selectively removable frame and a drag reduction member. The selectively removable frame can adapt to conform to at least one of the width or height of the land vehicle, and can be secured thereto by a securement assembly. In one embodiment, the drag reducing system can be folded and collapsed for compact storage. The drag reducing system can be easily and quickly secured to the back end of a semi-tractor trailer without tools and without requiring that any permanent modifications be made to the trailer. In one embodiment, drag reducing system includes a hinge joint assembly to facilitate installation, removal, and repositioning of drag reducing system.