This paper describes an injury criteria model implemented in computer language, and a restraint system effectiveness index for evaluating the degree to which the vehicle environment can prevent or reduce occupant injuries. The need for criteria of this type is based on the fact that if the degree of protection offered to a vehicle occupant by a restraint system or a vehicle interior (a function of the distribution and magnitude of the forces transmitted to the occupant) could be expressed in quantitative terms, then, more meaningful comparisons could be made between restraint configurations, and, areas of needed biomechanical research and statistical accident investigations could be more readily identified on the basis of the sensitivity of the results when the injury or effectiveness criteria are applied. The injury criteria model consists of three parts:​

1. An injury rating based on available human tolerance data including type of injury, seriousness, and magnitude of physical quantities such as force and acceleration which are related to injury production.
2. A relative motion criterion based on the extent to which adjacent body segments can move with respect to one another.
3. An index giving the probability of the crash event being studied. The analytical effectiveness index is hypothesized to be a function of the parameters defining a restraint environment (occupant, vehicle interior and restraints, and crash definition), the probability that an occupant will be using the vehicle location for which the restraint system is provided, and the probability that the restraint system will be in use by the occupant. The models are based on an extensive review of the literature and examples of their use given.