Federal Motor Vehicle Safety Standards; Head Restraints

This document completes the agency's response to petitions for reconsideration of the December 2004 final rule upgrading our head restraints standard. We are partially granting and partially denying the petitions. We are making two changes related to the backset requirement. First, to address concerns about variability in measurements, we are specifying that backset is determined by taking the arithmetic average of three measurements, rather than using a single measurement. Second, we are slightly relaxing the backset requirement by specifying that the 55 mm backset limit applies with the seat back at the vehicle manufacturer's specified design angle rather than at 25 degrees. This decision reflects consideration of interrelated issues and data concerning the 55 mm backset limit, consumer comfort, and seat back angle. In addition, we are making a number of other amendments. We are making changes related to non-use positions of rear seat head restraints, requirements for gaps between the head restraint and seat back, and the backset and height retention (lock) tests, as well as a number of changes in other areas. For the front seat requirements, we are providing one additional year of leadtime and also establishing a one-year phase-in with an 80 percent requirement. The agency previously delayed the compliance date for voluntarily installed rear outboard head restraints by two years. In this document, we are also establishing a one-year 80 percent phase-in for those requirements. Finally, we respond to a petition for rulemaking concerning requirements included in the upgraded head restraints rule. Today's amendments will not affect the costs of the December 2004 final rule. However, the agency estimates that the change in seat back angle to provide greater flexibility with respect to backset will result in a 20 percent reduction in the number of whiplash injuries prevented by upgraded front seat head restraints, compared to the benefits estimated in the December 2004