Belt Fit and Belt Torso Contact of Children on Belt-positioning Boosters

Principal Investigator: Randee Hunter, PhD, The Ohio State University


Previous studies show that lack of contact between seat belts and children’s torsos on belt-positioning booster seats (BPBs) may lead to belt slip-off during evasive vehicle maneuvers, increasing injury risk. However, current BPB belt fit measures do not quantify belt gap with the torso, and updated measures may help to further discriminate between designs which provide good vs. poor dynamic outcomes. This motivated us to investigate if different BPB designs produce varying amounts of gap between the belt and the torso.

We investigated 10 different BPBs and three seat belt anchor positions on a rear vehicle seat with 50 children and four ATDs. Using a 3D coordinate measurement system, we calculated two conventional measures of belt fit (shoulder belt score and lap belt score) and four novel measures of belt gap: gap size (the distance between the belt and the torso), gap length (the length along the seat belt where a gap was present), percent torso contact, and gap location.


Across the BPBs investigated, the belt fit and belt gap measures varied; for example, gap size ranged from 0–7 cm and gap length ranged from 0–32 cm. There was no specific type of BPB associated with a large gap size; however, the design of the belt guides on the lower inboard side contributed the most to the amount of gap. Most notably, the conventional belt fit metrics were not necessarily correlated to the belt gap outcomes, suggesting that different BPB design features influenced belt fit versus belt gap metrics.

belt fit and belt torso contact
These photos show two belt-positioning boosters with gap (left) versus no gap (right).


This study looked at belt fit metrics in a new way that relates to BPB design features, specifically how the belt is placed and the amount of belt contact against the torso. Understanding this will help to increase knowledge of good belt fit, providing implications for future studies.


We would like to use the BPBs selected for this study to investigate the influence of naturalistic seating postures on belt fit and how belt fit might influence dynamic outcomes during crashes.


Gretchen Baker, MS, The Ohio State University


Aubrie Sanchez, The Ohio State University; Akshara Sreedhar, The Ohio State University; Angela Tesny, The Ohio State University; Molly Tillis, The Ohio State University; Yadetsie Zaragoza-Rivera, The Ohio State University

IAB Mentors

Bill Lanz, American Honda Motor Co., Inc.; Mark Will, Britax Child Safety Inc.; Emily Thomas, Consumer Reports; Suzanne Johansson, General Motors Holdings LLC; Josh Gazaway, Graco Children’s Products Inc.; Mark LaPlante, Graco Children’s Products Inc.; Jerry Wang, Humanetics Innovative Solutions Inc.; Jason Stammen, National Highway Traffic Safety Administration; Schuyler St. Lawrence, Toyota USA; Julie Kleinert, Technical Advisor; Uwe Meissner, Technical Advisor