Effect of Class I–III obesity on driver seat belt fit

Abstract

Objective

Approximately 40% of the U.S. adult population are obese. An issue associated with this trend is proper seat belt fit for obese occupants. This study extends previous research, in which few individuals with high BMI (> 40 kg/m²) were included, by examining the relationship between participant and belt factors on belt fit for drivers with Class I-III obesity.

Methods

Posture and belt fit of 52 men and women with BMI from 31 to 59 kg/m² (median 38 kg/m²) were measured in a laboratory vehicle mockup. Five seat belt configurations were achieved by manipulating the belt anchorage locations. Body and belt landmark locations were recorded using a three-dimensional coordinate measuring machine.

Results

Higher BMI was associated with a lap belt position further forward and higher relative to the pelvis. On average, the lap belt was positioned an additional 32 mm forward and 13 mm above the ASIS with each increasing level of obesity classification. Sex had a small effect after accounting for BMI and stature. The mean fore-aft location of the lap belt was 24 mm more forward for men vs. women and 12 mm higher for women vs. men at the same stature and BMI. On average, women used 50 mm more belt webbing in the lap and 92 mm more in the shoulder vs. men.

Conclusions

The results suggest that increasing levels of obesity class effectively introduces slack in the seat belt system by routing the belt further away from the skeleton. Because the belt is designed to engage the pelvis during a frontal crash, belt placements that are higher and further forward may increase injury risk by allowing excursions or submarining. Unique to this cohort, sex had an important effect on belt fit measures after taking into account stature and BMI. The participant and belt factors considered explained only about 40% of the variance in belt fit. The remaining variance may be due to preference or exogenous body shape effects. Further research is needed to assess methods for enhanced seat belt fit for people with obesity, including addressing sex differences in belt routing.

Keywords:

• Obesity
• bariatric
• women
• seat belt
• restraint system
• occupant protection

Acknowledgments

The authors would like to thank all the participants who volunteered for this study. We would also like to acknowledge Bruce Bradtmiller of Anthrotech who provided guidance on application of standard anthropometric techniques for individuals with high BMI. The authors are also grateful to Laura Malik, Emily Lancaster and Rebecca Bubenheimer and the team of students who assisted in both data collection and data processing.

Additional information

Funding

This work was supported in partially funded by the University of Michigan-Ford Motor Company Alliance and the Center for Advancing Transportation Leadership and Safety (ATLAS). The ATLAS Center is supported by a grant from the U.S. Department of Transportation, Office of the Assistant Secretary for Research and Transportation, University Transportation Centers Program (DTRT13-G-UTC54). The ATLAS Center is a collaboration between the University of Michigan Transportation Research Institute (UMTRI) and the Texas A&M Transportation Institute (TTI).