Crash test dummy tests should be conducted to determine the optimum spool friction coefficient for each speed of a head on collision.
Automobile safety belts that spooled out upon accident impact would seem to prevent whiplash better than ones that held your torso firm and allowed your head to fly forward. A friction spooled safety belt would ease the forward impact and therefore likely prevent a more violent back thrust of the head and neck.
The friction coefficient could be adjusted to optimized spool out under various hypothetical crash speeds to lessen injury at each speed.
Background: Neck injuries from whiplash have long lasting effects.
And for all I know some may be made that way already.
Copyright 2012 Thomas Paul Murphy