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This paper investigates the role that load-limiters play with respect to the performance of occupant protection systems, with focus on performance in frontal crashes. Modern occupant protection systems consist of not just the seat belt, but also airbags, interior vehicle surfaces and vehicle structure. Modern seat belts very often incorporate load-limiters as well as pretensioners. Published research has established that load-limiters and pretensioners increase the effectiveness of occupant protection systems. Some have argued that load-limiters with higher deployment thresholds are always better than load-limiters with lower deployment thresholds. Through testing, modeling and analysis, we have investigated this hypothesis, and in this paper we present test and modeling data as well as a discussion to this data and engineering mechanics to explain why this hypothesis is incorrect.

The performance of two types of forward facing child restraint systems (CRSs), belt-positioning boosters (BPBs) and CRSs with an integral 5-point harness were compared in frontal and side-impact testing. Performance criteria in frontal impacts (head injury criteria (HIC), chest acceleration, head excursion and knee excursion) was evaluated by comparing a large set of NHTSA-run FMVSS 213 compliance test data generated with the 3-year-old-sized anthropomorphic dummy (ATD). Side-impact performance was evaluated by conducting a series of sled tests and comparing the relative head excursion of a 3-year-old-sized ATD. FMVSS 213 compliance test data shows that the average HIC, chest acceleration, and head and knee excursions are comparable for BPBs and harness CRSs. ATDs in BPBs experienced a slightly higher average HIC, and a slightly lower average head excursion than ATDs in harness CRSs without a tether.