In 1996 the National Highway Traffic Safety Administration set new standards (FMVSS No. 223 and 224) for rear impact guards on trailers and semitrailers built on or after January 26, 1998. But those regulations apply only to trailer and component manufacturers, FHWA notes, thus it is changing federal safety requirements to assure continued compliance by vehicle owners. The agency said, however, that "there is insufficient accident, cost, and research" to support retrofitting requirements for older trailers and that "the obstacles to obtaining such data are essentially insurmountable."
The final rule was published in the September 1 Federal Register, which can be accessed at http://www.access.gpo.gov/su_docs/aces/aces140.html.