Background Some safety belts may be more effective than others. Two technologies for improving the performance or use of belts are widely available as of 2003. Although they are not mandatory for meeting NHTSA standards, the agency regards them with favor and provides consumer information on their availability, by make-model, in Buying a Safer Car. Safety belt pretensioners (installed on 63 percent of MY 2002 light vehicles) retract the safety belt to remove any slack almost instantly in a crash. Load limiters (installed on 84 percent of MY 2002 light vehicles) prevent belt forces from reaching unsafe levels by causing parts of the safety belt to stretch or deform at a predetermined, safe force level. NHTSA's Phase 1 evaluation shows that the combination of pretensioners and load limiters significantly reduces HIC, chest acceleration, and chest deflection scores on 35 mph frontal NCAP tests.
Objectives Compare the overall fatality- and serious injury-reducing effectiveness of conventional safety belts and the effectiveness of belts equipped with one or more of these improvements - in all crashes and in frontal crashes. Estimate the effect of pretensioners and load limiters on fatal and serious head, chest, and abdominal injuries. Look at the effectiveness of each technology by seating position, to determine whether they perform differently.
Proposed Approach Information will be obtained from NHTSA's Buying a Safer Car about the initial installation dates of these technologies, by make-model, and manufacturers will be contacted if necessary for clarification. Statistical analyses of FARS data, such as double-pair comparison analyses, will be used to estimate overall belt effectiveness before and after the introduction of the belt improvements - in all crashes and in frontal crashes. Injury rates by body region, before and after the belt improvements, will be compared in NASS data and in the enhanced FARS file that includes cause-of-death information.
Status The Phase 1 evaluation, "NCAP Test Improvements with Pretensioners and Load Limiters" was published in March, 2003. The evaluation may require 2-3 years until sufficient FARS data accumulate.