Technical tools to describe the crash severity of a vehicle are the delta-v of the center of gravity of the vehicle considered and the EES value of the deformation. In a collision without glance-off, such as a barrier impact with 100 % overlap, EES and delta-v are of similar values. If glance-off occurs in an impact with only partial overlap, the EES can be considerably higher than the delta-v, especially with high collision speeds. The theoretical background is standard knowledge for engineers dealing with accident reconstruction. However, scientists in the biomechanical and medical area are less aware of the difference of the two terms, sometimes using them as synonyms even in accident samples with all kinds of collision types. This can result in significant misinterpretations of the biomechanical and medical findings in their study. Mechanisms of severe injuries have to be divided into those with extensive intrusions, described by the EES, and into those without intrusion but high inertial loading, caused by a high delta-v. Several examples are shown where just "looking at the car photo" leads to an enormous error in the judgement of the delta-v.
A large amount of instrumented crash tests has visualised the theoretical calculations in practice; more such tests will be carried out documenting the difference of collision speed, delta-v and EES in various collision angles and overlap values, also in pure side impacts. Moreover the test results have been be simulated by mathematical accident reconstruction tools.