Abstract
This paper presents an overview of NHTSA's vehicle aggressivity and fleet compatibility research activities. This research program is being conducted in close co-operation with the International Harmonised Research Agenda (IHRA) compatibility research group. NHTSA is monitoring the changing vehicle mix in the U.S. fleet, analysing crash statistics, and evaluating any implications that these changes may have for U.S. occupant safety. NHTSA is also continuing full scale crash testing to develop a better understanding of vehicle compatibility and to investigate test methods to assess vehicle compatibility.