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Correctly fitted seat belts save the lives of car passengers everyday. In attempt to reduce the risk of injuries, primarily abdominal, caused by inappropriate belt fitting, Transport Canada developed the Belt fit Test Device (BTD). The BTD is a physical hardware measuring device that tests whether the lap and torso belt are appropriately positioned with respect to the bony structures of the pelvis and rib cage of the restrained occupant. To overcome the deviations of hardware physical tests and to enable review of belt design in early design phases, the Alliance of Automobile Manufacturers funded the development of an electronic simulation and modeling tool in the form of an electronic Belt fit Test Device (eBTD). The development takes place in close co-operation with the Joint Working Group on Abdominal Injury Reduction (JWG-AIR).

In 1997 Mertz, Prasad and Irwin [1] have described a technique for the development of injury risk curves for measurements made with the CRABI and Hybrid III family of biofidelic child and adult dummies that are used to evaluate restraint systems in frontal collision simulations. They further developed normalized injury risk curves for neck tension, neck extension moment, combined neck tension and extension moment for adults and children. The approach described by Mertz et al [1], is based on lines of equivalent stress and uses the maximum normal stress theory of failure to impose limits of the risk of injuries. In this paper a complementary approach is described based on the maximum energy of failure and lines of constant energy. A special case of this approach in 1D is used to develop the assessment values obtained by Mertz et al [1]. Limitations and advantages of the energy based approach are described, with especial emphasis on future implementation.