Compatibility of Belt-positioning Boosters in Vehicles

Principal Investigator: Julie Bing, MS, The Ohio State University

Below is an executive summary of this project. Please note that this summary describes results and interpretation that may not be final. Final interpretation of results will be in the peer-reviewed literature.

At left: 27.9 percent of the booster installations were predicted to have too obtuse a seat back to seat bottom angle compared to the vehicle seat.At right: Seat belt anchors which are too close together can push the booster off-center from the intended position (pictured); this scenario had a predicted occurrence rate of 65.3 percent in the center positions of rear seats.

Belt-positioning boosters are effective at preventing injuries in children, but the incorrect use of boosters is a persistent problem. Many efforts have been made to address the booster misuse issue, including legislation and educational campaigns. However, little research has examined the booster’s compatibility with the vehicle seat and incompatibility may be a contributing factor for high booster misuse rates. This study aimed to increase proper belt-positioning booster usage by better understanding the physical factors involved, and to develop a resource for benchmark booster/vehicle seat dimensions to help guide industry in design decisions.

Comprehensive measurements were collected from 40 boosters and 95 seating positions from 50 modern vehicles, which included both left outboard and center seating positions in the rear row(s).  Key dimensions of each booster were compared to corresponding dimensions in vehicles to predict the rate of incompatibilities across all 3,800 potential booster/vehicle combinations.  To validate the results, 72 physical booster installations were completed and the rate of predicted incompatibilities within this subset was compared to the actual incompatibilities observed during installation.  From the validation data, tolerances and correction factors were determined for each fit criterion and the accuracy, sensitivity, and specificity of all predictions were calculated.

The interaction between the base of the booster and the vehicle seat belt buckle was found to be the most common predicted incompatibility, at a rate of 14.6 percent of outboard installations and 65.3 percent of center installations. This can result in the booster being pushed off-center from the intended seating position by 2 to 15 cm.

Head restraint interference was predicted in 22.8 percent to 29.1 percent of high back booster installations, depending on the position of the booster’s adjustable head support.  Vehicle head restraints with gently sloping surfaces along their bottom edge were more accommodating of booster seats, as compared to head restraints with sharply protruding bottom edges. Mismatches between booster back angles compared to vehicle seat back angles occurred in 28.5 percent of predicted combinations.  As evidenced in the accompanying graphic, the overwhelming majority of angle incompatibilities resulted from the seat back to seat bottom angle of the boosters being more obtuse than the vehicle seats.

This study quantified some of the more common incompatibilities between boosters and vehicles, which may complicate booster usage for typical caregivers. These data can serve as a critical reference for industry design decisions, including prioritization of specific problem areas. 


Laura Jurewicz, The Ohio State University

IAB Mentors

Angela Manning, American Honda Motor Co., Inc.; Keith Nagelski, Britax Child Safety, Inc.; Eric Dahle, Evenflo Company Inc.; Julie Kleinert, General Motors Holdings LLC; Jason Carpenter, Graco Children’s Products Inc.; Mark La Plante, Graco Children’s Products Inc.; Tim Patrizi, Graco Children’s Products Inc.; John Combest, Nissan Technical Center North America Inc.; Barbara Birkenshaw, Volkswagen Group of America; Uwe Meissner, Technical Advisor 

Publication References