; and (2) to improve motor carrier and passenger motor vehicle safety. 3. Definitions Section 30102(a) of title 49, United States Code, is amended— (1) in the matter preceding paragraph (1), by striking chapter— and inserting chapter: ; (2) by redesignating paragraphs (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), and (13) as paragraphs (2), (3), (4), (5), (7), (8), (9), (10), (11), (12), (15), (20), and (22), respectively; (3) by inserting before paragraph (2) (as so redesignated) the following: (1) comprehensive underride protection system means all of the front underride guards, rear underride guards, or side underride guards, as applicable, installed on a motor vehicle. ; (4) by inserting after paragraph (5) (as so redesignated) the following: (6) front underride guard means a device installed on or near the front of a motor vehicle that prevents or limits the distance that a vehicle struck by the vehicle with the device will slide under the front of the striking vehicle. ; (5) by inserting after paragraph (12) (as so redesignated) the following: (13) passenger motor vehicle has the meaning given that term in section 32101. (14) rear underride guard means a device installed on or near the rear of a motor vehicle that prevents or limits the distance that the front end of a vehicle striking the rear of the vehicle with the device will slide under the rear of the impacted vehicle. ; (6) by inserting after paragraph (15) (as so redesignated) the following: (16) Secretary means the Secretary of Transportation. (17) semi-trailer means a trailer, other than a pole trailer, which is designed to rest upon, or be carried by, a motor vehicle. (18) side underride guard means a device installed on or near the side of a motor vehicle that prevents or limits the distance that the front end of a vehicle striking the side of the vehicle with the device will slide under the side of the impacted vehicle. (19) single unit truck means a truck (excluding any attached trailer).