Rear occupant protection in rear crashes is a complex issue. Structural intrusion has been shown to be a significant factor in the injury mechanism of second-row children. In this study, a new model was developed to help quantify dynamic second-row intrusion, in terms of displacement, velocity, and acceleration, and assess its effect on rear occupant responses as a function of time.

A mathematical model was developed using crash test data based on two reconstructed field accidents involving two different rear-ended vehicles with second-row children. The model also used the corresponding FMVSS 301R-type rear barrier tests of a similar vehicle.

The crash test pulse data and videos from FMVSS 301R-type tests were analyzed to determine the timing and magnitude of second-row intrusion. Crash tests that had been conducted to simulate the field accidents were then used to validate the model. These tests included instrumented ATDs (Anthropometric Test Device) seated in the second-row area of the struck vehicles. The biomechanical responses were used to assess the validity of the mathematical model.

Comparison between the mathematical model and the test data showed good agreement. For example, the model correctly showed that the dynamic second-row intrusion was greater than residual/static intrusion/displacement. The model also predicted accelerations that were in good agreement with the test data.

Video analysis and head/chest acceleration time histories of the ATD’s indicated that intrusion occurred early and was an important factor in the occupant responses. Both the extent and velocity of dynamic intrusion also influenced the biomechanical responses.

The model predicted head and chest accelerations that were greater than the overall vehicle accelerations due to localized structural intrusion.

The mathematical model developed in this study is a first to assess the dynamic effect of second-row intrusion on rear occupant responses. Identifying factors that influence injury mechanisms are important when assessing the potential effectiveness of countermeasures.

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