SUMMARY: This NPRM proposes to upgrade the Federal motor vehicle safety standards that address rear underride protection in crashes into trailers and semitrailers. NHTSA is proposing to adopt requirements of Transport Canada??s standard for underride guards@ which require rear impact guards to provide sufficient strength and energy absorption to protect occupants of compact and subcompact passenger cars impacting the rear of trailers at 56 kilometers per hour (km/h) (35 miles per hour (mph)). NHTSA is issuing this NPRM in response to a petition for rulemaking from the Insurance Institute for Highway Safety (IIHS)@ and from Ms. Marianne Karth and the Truck Safety Coalition (TSC). This is the second of two documents issued in response to the Karth/TSC petition. Earlier@ NHTSA published an advanced notice of proposed rulemaking requesting comment on strategies pertaining to underride protection afforded by single unit trucks