Vehicle to vehicle rear impact crash tests and sled buck tests were run to evaluate seat system performance related to Hybrid III surrogate response and comparison with NHTSA proposed combined load injury assessment values, as well as standard injury criteria. The crash and sled buck test impact conditions were modeled after actual case study incidents where changes in the rear impacted vehicle speeds ranged from about 25 to 50 kph. With the exception of one baseline vehicle-to-vehicle rear impact test, the dynamic tests provided side-by-side comparisons, and test-to-test evaluations, of surrogate response in conventional yielding front seats versus much stronger seat systems such as the belt integrated seat designs. Head, neck and chest injury criteria were used in the evaluations, including both the proposed NHTSA combined load neck criteria and SAE J 885 injury values. The surrogate response injury levels for the conventional yielding seats correlated well with the actual case study injury results. The seat comparison response generally indicated much reduced head and neck injury potential to surrogates seated in the stronger seat designs. The dynamic tests also demonstrate the importance of testing within the full vehicle interior structure to insure that floor strength is compatible with seat strength, so as to attain optimum occupant protection in stronger seat designs, and to assess injury risk to occupants in yielding or collapsing seat designs, as well as rear seated occupants, such as children. The tests indicate that quasi-static seat strength measurements made with more realistic “torso body block” load devices can provide reasonable estimates on the ultimate failure modes and dynamic load capabilities of the seat systems if the seat systems are properly mounted to the vehicle. Quasi-static seat strength results are presented for a variety of conventional collapsing seat designs and stronger seat systems like the belt integrated designs. One sled buck test was run with a rear-seated child surrogate to demonstrate the hazard of front seat collapse into the rear seat occupant area. The results of these tests further demonstrate the need for dynamic testing to assess total seat system performance and full occupant protection in rear impacts.