Optimizing protection for rear seat occupants : assessing booster performance with realistic belt geometry using the hybrid III 6YO ATD.

Klinich, Kathleen D.; Reed, Matthew P.; Manary, Miriam A.; Orton, Nichole R.; Rupp, Jonathan D. · 2011 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This study addresses the challenge of optimizing rear seat protection for children aged 6 to 12, who often experience poor seat belt fit due to vehicle seat geometry. As booster seat usage increases, vehicle designs must accommodate children both with and without boosters. The research investigates how realistic belt geometries and seating postures affect crash kinematics, specifically looking for trade-offs in belt fit that might arise when designing for both restrained and unrestrained child occupants. The researchers conducted a series of sled tests using the Hybrid III 6-year-old Anthropomorphic Test Device (ATD). The experimental design included 12 tests with the standard ATD and 29 tests with a modified ATD featuring a more realistic pelvis shape, flesh stiffness, and a gel abdomen. Four booster seats providing a range of static belt fits were tested. Variables included shoulder belt upper anchorage locations (standard, 64 mm inboard, and 64 mm outboard) and lap belt anchorage locations representing shallow (rearward) and steep (forward) angles permitted under FMVSS 210. Additionally, two seating procedures were compared: the standard FMVSS No. 213 procedure and an alternate UMTRI procedure designed to produce postures closer to those of actual children. Key findings indicate that kinematic results for the standard and modified dummies were more similar than expected, though the modified dummy was less sensitive to lap belt geometry than its prototype version. The seating procedure had a significant impact on outcomes; the UMTRI procedure resulted in greater knee-head excursion differences and less forward torso rotation compared to the FMVSS No. 213 procedure. Regarding belt geometry, shifting the shoulder belt anchorage laterally produced minimal kinematic variations, largely because booster seat belt-routing features limited differences in static shoulder belt fit. However, moving the lap belt anchorage from a rearward (shallow angle) to a forward (steep angle) position produced less desirable kinematics across all booster seats. The forward anchorage allowed greater forward translation of the booster and ATD before the belt engaged the pelvis. The study concludes that while steeper lap belt angles are associated with better fit for children sitting without boosters, they degrade performance for those using boosters. This suggests a performance trade-off in vehicle design, as rear seat belts optimized for unrestrained children may compromise the safety of children using booster seats. The findings highlight the importance of considering realistic belt geometries and child postures when evaluating child restraint systems.

Key finding

Moving the lap belt anchorage from a rearward position with a shallow angle to a forward position with a steep angle produced less desirable kinematics with all booster seats tested.

Methodology

simulator

Sample size: 41

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• child passenger safety