The Federal Motor Vehicle Safety Standard (FMVSS) Number 208 establishes quantitative criteria for automobile occupant injury, as determined by use of anthropomorphic test devices. For the head, the criterion is a severity index of 1000, calculated according to a weighted-impulse method commonly known as the Gadd Severity Index (GSI).

The biomechanical problem of establishing a comprehensive tolerance criterion for head injury has long been of interest. Since this is a relatively unknown area, many assessment methods have been conceived. These methods can be classified into three categories:​ the severity index, the brain-skull model, and the brain model. Most of the assessments were based upon the Wayne State Tolerance curve.

In a recent paper, a comparison of two well-known methods for estimating internal head injury hazard was presented. The first method, proposed by C.W. Gadd, is a weighted impulse-integration procedure;​ the second method, proposed at the Vienna Institute of Technology, is based on the absolute value of the maximum displacement of a brain when represented by a single degree-of-freedom vibration model. Some of the assumptions upon which those methods are based will be discussed in this paper. The object of this paper is to analyze those two methods and to present improved measurements of internal head injury hazard.