; and (4) appendix G to subchapter B of chapter III of title 49, Code of Federal Regulations— (A) by redesignating paragraphs 6 (relating to safe loading) through 14 (relating to motorcoach seats) as paragraphs 7 through 15, respectively; and (B) by inserting after paragraph 5 (relating to lighting devices) the following: 6. Rear impact guards and rear end protection Any trailer or semitrailer required under section 393.86 to be equipped with a rear impact guard or rear end protection— (A) that does not meet the requirements under section 393.86; (B) that— (i) is missing; or (ii) has— (I) any metal perforated by rust or corrosion that compromises structural integrity; (II) a cracked weld; (III) a cracked or fractured vertical member; (IV) a cut or tear in any underride guard component; or (V) a missing fastener or a loose fastener; or (C) for which the dimensional integrity of the guard or protection is compromised. . 5. Research and periodic review of underride guard standards (a) Request for Proposals As soon as practicable, the Secretary of Transportation shall issue a Request for Proposals for the design of 2 high capacity rear underride barrier prototypes of a generic guard (with energy absorption and without energy absorption) to prevent underride crashes and protect motor vehicle passengers against severe injury at crash speeds of up to 65 miles per hour. (b) Evaluation The Secretary shall— (1) evaluate the proposals received in response to the Request for Proposals issued pursuant to subsection (a)