Compatibility is an issue that relates to the improvement of vehicle safety. After frontal and side impact self protection, partner protection, a key component of compatibility, represents the next step forward for passive safety improvement. Compatibility is complicated to achieve, because it requires world-wide industry to take steps in a similar direction. A harmonized approach is difficult to achieve because many differences in vehicle makes and models between the various fleets around the world exist. This leads to incompatibilities between vehicles in a global sense:​ Asian markets have a high market share of very small cars, the American market is characterized by a high proportion of LTVs and SUVs and the European market is somewhere between the American and the Asian markets.

It is obvious that a lot of requirements need to be fulfilled by a compatibility regulation which is;​ beneficial to the customer, which is scientifically meaningful, refers to front and side-impact and which is applicable for all markets and, last but not least, is considered to be fair by all manufacturers.

ACEA is not in the position to suggest a solution meeting all these requirements. However, some test results and observations which could contribute to a solution are presented in this paper.

The focus of most proposed compatibility procedures is to improve structural interaction in collisions involving passenger cars. A couple of conditions exist that influence the definition of a geometric zone for structural interaction. A zone for structural interaction has to ensure maximal interaction between passenger vehicles with other passengers vehicles, SUVs/LTV’s and trucks (to be supported by under-run protection systems) can be achieved. This could represent a first step in increasing compatibility within vehicle fleets. Structural interaction is, in fact, the principle requirement for compatibility before the issue of stiffness can be solved. Keeping this in mind, ACEA drafted a road map chartering the path toward improved compatibility, which is presented in this paper.