The Traffic Accident Reconstruction Origin -ARnews-

Re: Seat Belt Operation

Gene K. Baxter (baxter@forensicgroup.com)
Fri, 9 Jan 1998 01:10:21 -0500 (EST)

Based on that Delta-V, and using a time duration of 100 milliseconds or so you can determine the g-force (peak is about 2 times the average g-force) and, from that and the weight of the driver, estimate the force that was applied to the belt during the impact. You may even want to treat his upper torso and lower body as separate loads to the shoulder and seat belt, respectively. Then, using the geometry of the belt system on the seated driver, the allowable "stretch" (in/lb) as specified in the Federal Motor Vehicle Safety Standards, an estimated "slack" that would normally be in the belt, a estimated "spool out" for the type of seat belt retractor installed, and an estimated "compression of the sternum" for the forces involved, you can estimate how far forward the person could have moved during the impact. Include the effect of his forward head rotation and compare all that motion to the geometry of the vehicle at the drivers position and you should be able to estimate whether or
not his head would hit the windshield and, if so, how far through the windshield it could have gone. It will be relatively easy to visualize all this by making a simple cardboard and pin model, like a simplified anthropometric model, of the driver seated in the vehicle and, then, demonstrate his possible forward motion during the collision. I hope this helps and gives you some additional ideas for resolving your question.
Gene K. Baxter
baxter@forensicgroup.com

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