An automotive accident occurred in which two vehicles of nearly the same mass collided head-on, in a manner resembling a fixed-barrier frontal collision test. However, this was an actual on-the-road accident and not a test crash, and both vehicles sustained damages of approximately the same severity. One of the two unrestrained drivers sustained internal thoracic hemorrhaging, and the other received a light chest contusion.

In order to clarify differences between the injuries sustained by the two occupants, we conducted a detailed case study and analysis of this particular traffic accident. We estimated external forces [deceleration, SI (Severity Index), load, and load per unit area] exerted on both drivers, and examined how differently these forces were applied and what factors caused this difference. These points were determined in a sled test of the steering system and in an actual vehicle test, usig a dummy in both tests.

As a result of our study, we have put forth a theory regarding the factors and values of human body survival l i m i t s . In so doing, we have raised a question as to the safety of the steering system, and as to previous evaluations of that safety.