; (7) by inserting after paragraph (20) (as so redesignated) the following: (21) trailer means a vehicle, with or without motive power, that is designed— (A) to carry persons or property; and (B) to be drawn by a motor vehicle. ; and (8) by inserting The term after the paragraph designation in each of paragraphs (1) through (22) (as so redesignated). 4. Underride guard rulemaking (a) In general Subchapter II of chapter 301 of title 49, United States Code, is amended by adding at the end the following: 30129. Underride guards (a) Rear underride guards (1) In general Not later than 1 year after the date of enactment of this section, the Secretary shall issue a final rule to require the installation of rear underride guards that meet the performance standards described in paragraph (3) on— (A) any trailer with a gross vehicle weight rating of 10,000 pounds or more that is manufactured on or after the effective date of the rule; (B) any semi-trailer with a gross vehicle weight rating of 10,000 pounds or more that is manufactured on or after the effective date of the rule; and (C) any single unit truck— (i) the bottom of the carriage of which is greater than 22 inches above the ground; (ii) with a gross vehicle weight rating of 10,000 pounds or more; and (iii) that is manufactured on or after the effective date of the rule. (2) Retro-fit requirements Not later than 2 years after the date of enactment of this section, the Secretary shall issue a final rule requiring the installation of rear underride guards that meet the performance standards described in paragraph (3) on— (A) any trailer with a gross vehicle weight rating of 10,000 pounds or more that is manufactured before the effective date of the rule under paragraph (1); (B) any semi-trailer with a gross vehicle weight rating of 10,000 pounds or more that is manufactured before the effective date of the rule under paragraph (1); and (C) any single unit truck— (i) the bottom of the carriage of which is greater than 22 inches above the ground