The wearing rate of standard 3-point seat belts by front seat car occupants in the Netherlands is about 70%. Field studies have shown that about 1/3 are used incorrectly. So approximately 50% of the front seat occupants are not or insufficiently protected by their seat belts.
The influence of incorrect use or misuse on the seat belt effectiveness has been studied by the TN0 Crash-Safety Research Centre in an extensive research programme. Eight full-scale tests have been performed with a car body mounted on an impact sled. The influence of variations in seat position and belt routing on adult and child dummy responses are studied. The effect of an additional driver airbag system on the dummy loadings is also analyzed in this programme.
The results of this test programme are presented in terms of Ride-Down-Effect RDE), dummy velocity-displacement curves, dummy contact with the car interior and injury criteria. The injury criteria of the individual body parts are combined into one overall value. Injury probability analysis has been used to evaluate the effect of misuse configurations.
It is concluded that certain misuse configurations extremely reduce seat belt effectiveness. A clear understanding of the type of misuse and the effect on occupant injuries have important implications for the design of protection systems, community actions (e.g. governmental campaigns) and legislation.