The Influence of the Seat Belt Tension Reliever Feature on Seat Belt Usage and Injury Severity

In an effort to encourage greater usage of the newly introduced integral lap and shoulder belt for outboard front seat occupants during the 1970's, a tension reliever device was designed into the shoulder belt retractor. The purpose of the tension reliever was to reduce the pressure on the shoulder and upper torso of the seat belt wearer caused by the retractor pulling on the belt webbing.

The relative merit of this device has been questioned, but never resolved. A study of Chrysler built cars involved in frontal impact accidents was made to compare the frequency of seat belt usage and the relative injury severity in comparable size passenger cars before and after the introduction of the tension reliever.

The result of this study shows (1) an increase in seat belt use in the cars equipped with a tension reliever during a time when seat belt use in all cars was relatively unchanged, and (2) the relative injury to belt wearers was less severe in cars equipped with the tension reliever.