18. Biomechanics of Automotive Safety Restraints

There is an advertising poster put out in 1940 by the now defunct Packer Motors that suggested an unusual way for the right front passenger to protect him/herself before an impending crash. The ad suggested that the passenger in the “dead man’s seat” curl up in the footwell to ride out the crash. This is possible for a small person in a large car but it is not a practical suggestion because by the time the passenger manages to get into the footwell, the crash would have occurred already. The more practical form of protection is the use of automotive restraint systems. There are two forms of safety restraints. Seatbelts constitute the active restraint system which requires the occupant to actively participate in its use. There are forms of automatic seatbelts but so far their use has been limited. The most popular form of passive restraint is the airbag which is deployed at the time of the crash, hence the name passive restraint. Both systems afford good protection for the occupant but when used together, they are very effective in mitigating injuries and preventing fatalities. The biomechanics behind the use of these restraint systems is the subject of this chapter.