“This impact is intended to represent the most frequent type of road crash, resulting in serious or fatal injury. It simulates one car having a frontal impact with another car of similar mass”. (EuroNCAP frontal impact procedures).

It can be argued that human bodies are poorly prepared to support direct hits from hard objects. On the other hand, there are proofs of resistance to very high decelerations, provided they are held for extremely short periods of time. Yet, in front-to-front vehicle impacts, a third phenomenon that can be compared to direct hits takes place:​ instantaneous changes of speed.

Most modern vehicles are nowadays tested thoroughly to evaluate their capability to protect their occupants in case of frontal impacts. But these tests are performed under the premise that the vehicle is having an impact with another car of similar mass that is traveling at the same speed. These conditions lead to an incomplete analysis of the complex phenomena that take place in a real front-to-front vehicle since it is statistically improbable that a vehicle will crash with another one that has both the same mass AND speed —and in this scenario, the vehicle with the lesser kinetic energy will unfailingly suffer an instantaneous change of speed—.

This paper will confirm the lastly mentioned issue using basic physics models (namely mass-spring models), and will discuss the the way of combining structural integrity and occupant restraints to ensure the maximum possible protection. This will be done from a general and synergistic point of view, and will point out some aspects that should be developed thoroughly within the corresponding settings and using appropriate resources.