SUMMARY:Our safety standard on occupant protection in interior impact requires@ in part@ that light vehicles provide head protection when an occupant??s head strikes upper interior components@ such as pillars@ side rails@ headers@ and the roof during a crash. For altered vehicles and vehicles built in two or more stages@ these requirements become effective September 1@ 2006. The Recreation Vehicle Industry Association and the National Truck Equipment Association petitioned the agency to permanently exclude certain types of altered vehicles and vehicles manufactured in two or more stages from these requirements. This document responds to these petitions for rulemaking and proposes certain amendments to the standard.Based on a careful consideration of both the safety benefits of the upper interior protection requirements@ and practicability concerns relating to vehicles built in two or more stages and certain altered vehicles@ we are proposing to limit these requirements to only the front seating positions of those vehicles. Further@ we tentatively conclude that it is appropriate to exclude a narrow group of multi-stage vehicles delivered to the final stage manufacturer without an occupant compartment@ because of impracticability concerns.We are also proposing to delay the effective date of the head impact protection requirements as they apply to final stage manufacturers and alterers until September 1@ 2008.