; and (ii) to alert the operator of the vehicle of an impending collision; and (B) a crash-imminent braking function to provide automatic braking when forward-looking sensors of the vehicle indicate that— (i) a crash is imminent; and (ii) the operator of the vehicle is not applying the brakes. (2) Commercial motor vehicle The term commercial motor vehicle has the meaning given such term in section 31101 of title 49, United States Code. 4405. Underride protection (a) Rear underride guards (1) Rear guards on trailers and semi-trailers (A) In general Not later than 1 year after the date of enactment of this Act, the Secretary of Transportation shall issue such regulations as are necessary to revise motor vehicle safety standards under sections 571.223 and 571.224 of title 49, Code of Federal Regulations, to require trailers and semi-trailers manufactured after the date on which such regulation is issued to be equipped with rear impact guards that are designed to prevent passenger compartment intrusion from a trailer or semi-trailer when a passenger vehicle traveling at 35 miles per hour makes— (i) an impact in which the passenger vehicle impacts the center of the rear of the trailer or semi-trailer; (ii) an impact in which 50 percent the width of the passenger vehicle overlaps the rear of the trailer or semi-trailer