Effect of realistic vehicle seats, cushion length, and lap belt geometry on child ATD kinematics.

Klinich, Kathleen D.; Reed, Matthew P.; Ebert, Sheila M.; Rupp, Jonathan D. · 2011 · ROSA P / United States. Department of Transportation. National Highway Traffic Safety Administration

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Summary

This study investigates how realistic vehicle seat cushion lengths and lap belt geometries affect the crash kinematics of child anthropometric test dummies (ATDs). The research was motivated by the observation that many children aged 4–12 travel without booster seats, often sitting on rear seats with cushion lengths (median 455 mm) that exceed their thigh length. This mismatch causes slouching and poor lap belt fit, increasing the risk of submarining or rollout injuries. The authors aimed to determine if shortening seat cushions or altering belt anchorage locations could improve protection for children transitioning out of booster seats. The researchers conducted 13 sled tests using Hybrid III 6-year-old (6YO) and 10-year-old (10YO) ATDs mounted on real vehicle seats from Dodge Caravans. They varied two primary factors: cushion length (450 mm, representing production length, vs. 350 mm, a shortened length) and lap belt geometry (rear, mid, and forward anchorage locations corresponding to angles of 23°, 50°, and 75°). An updated seating procedure was employed to position the ATDs’ hips further forward on longer cushions, reflecting the slouched postures observed in child volunteers. Kinematics were evaluated using peak head and knee excursions, the difference between these excursions (knee-head excursion), and minimum torso angle. One additional test used a booster seat with the 6YO ATD for comparison. Results indicated that shortening the seat cushion improved kinematic outcomes, particularly for the 10YO ATD. Lap belt geometry had a more pronounced effect when using the longer cushion; mid and forward belt geometries produced better kinematics than the rearward geometry. The worst performance for both ATDs occurred with the long cushion and rearward lap belt, where clear submarining was observed. While shorter cushions and forward belt angles improved belt fit and reduced knee-head excursion, the improvements were smaller than those provided by a booster seat. Notably, none of the vehicle seat tests achieved the ideal kinematic target of a peak torso angle between -10 and -20 degrees, indicating that even optimized seat designs did not fully replicate the restraint performance of booster seats. The study concludes that while shortening rear seat cushions and optimizing lap belt geometry can improve occupant protection for children, especially those the size of the 10YO ATD, these modifications alone are insufficient to match the safety benefits of booster seats. The findings highlight a potential gap in protection for children who transition out of boosters, suggesting that current vehicle seating environments may not adequately accommodate older children without additional restraint systems. The authors caution that the 6YO ATD’s biofidelity limitations may underestimate submarining risks, implying that real children might be at greater risk than the test results suggest.

Key finding

Shortening the seat cushion length from 450 mm to 350 mm improved child ATD kinematics, particularly for the 10YO, whereas the combination of long cushions and rearward lap belt geometry caused submarining.

Methodology

simulator

Sample size: 13

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