This NPRM proposes to upgrade Federal Motor Vehicle Safety Standard (FMVSS) No. 223, “Rear impact guards,” and FMVSS No. 224, “Rear impact protection,” which together address rear underride protection in crashes into trailers and semitrailers. NHTSA is proposing to adopt requirements of the Canada Motor Vehicle Safety Standard (CMVSS) for underride guards (CMVSS No. 223, “Rear impact guards,”) that became effective in 2007. The CMVSS No. 223 requirements are intended to provide rear impact guards with sufficient strength and energy absorption capability to protect occupants of compact and subcompact passenger cars impacting the rear of trailers at 56 km/h (35 mph). As the current requirements in FMVSS Nos. 223 and 224 were developed with the intent of providing underride crash protection to occupants of compact and subcompact passenger cars in impacts up to 48 km/h (30 mph) into the rear of trailers, increasing the robustness of the trailer/guard design such that it will be able to withstand crash velocities up to 56 km/h (35 mph) represents a substantial increase in the stringency of FMVSS Nos. 223 and 224.

This NPRM also proposes to adopt Transport Canada’s definition of “rear extremity” to define where on a trailer aerodynamic fairings are to be located to avoid posing a safety hazard in rear underride crashes.

Rear underride crashes are those in which the front end of a vehicle impacts the rear of a generally larger vehicle, and slides under the rear-impacted vehicle. Underride may occur to some extent in collisions in which a small passenger vehicle crashes into the rear end of a large trailer or semi-trailer because the bed and chassis of the impacted vehicle is higher than the hood of the passenger vehicle. In excessive underride crashes, there is “passenger compartment intrusion” (PCI) as the passenger vehicle underrides so far that the rear end of the struck vehicle collides with and enters the passenger compartment of the striking passenger vehicle. PCI can result in severe injuries and fatalities to occupants contacting the rear end of the struck vehicle. An underride guard prevents PCI when it engages the striking end of the smaller vehicle and stops the vehicle from sliding too far under the struck vehicle’s bed and chassis.

The occupant crash protection features built into today’s passenger vehicles are able to provide high levels of occupant protection in 56 km/h (35 mph) frontal crashes. ⁽¹⁾ If guards were made stronger to remain in place and prevent PCI in crashes of severities of up to 56 km/h (35 mph), the impacting vehicle’s occupant protection technologies could absorb enough of the crash forces resulting from the impact to significantly reduce the risk of fatality and serious injury to the occupants of the colliding vehicle.

Link: http://www.regulations.gov/#!documentDetail;D=NHTSA_FRDOC_0001-1548