Changes to NCAP testing oblige the use of load limiters on safety-belts with lower threshold values that yield less thorax compression but also allow for greater forward displacement of the occupants. To address the greater forward displacement of rear occupants, UN R17 is under revision to require more stringent energy dissipation performance for those areas of the rear of seats (including the head restraints and parts mounted on the seat) where the head of the rear occupant may come into contact. UN R21 allows for alternative testing of the rear parts of seats (paras. 5.7-5.7.3. ) However, in light of the changes to UN R17, this alternative approach is no longer valid. This proposal would delete the alternate method and expands the scope of UN R21 to include testing of any parts mounted on the seats.