Effects of driver characteristics on seat belt fit

A laboratory study of posture and belt fit was conducted with 46 men and 51 women, 61% of whom were age 60 years or older and 32% age 70 years or older. In addition, 28% of the 97 participants were obese, defined as body mass index ≥ 30 kg/m^2. A mockup of a passenger vehicle driver's station was created and five belt anchorage configurations were produced by moving the buckle, outboard-upper (D-ring), and outboard-lower anchorages. An investigator recorded the three-dimensional locations of landmarks on the belt and the participant's body using a coordinate measurement machine. The location of the belt with respect to the underlying skeletal structures was analyzed, along with the length of belt webbing. Using linear regression models, an increase in age from 20 to 80 years resulted in the lap belt positioned 18 mm further forward relative to the pelvis, 26 mm greater lap belt webbing length, and 19 mm greater shoulder belt length. An increase in stature of 350 mm (approximately the range from 5th-percentile female to 95th-percentile male in the U.S. population) was associated with the lap belt 14 mm further forward relative to the pelvis, the shoulder belt 37 mm more outboard relative to the body centerline, and 38 mm less shoulder belt webbing length. Among the driver factors considered, body mass index had the greatest effects. An increase of BMI in 20 kg/m^2, which spans approximately the central 90% of U.S. adults, was associated with the lap belt being placed 102 mm further forward and 94 mm higher, relative to the pelvis, and increases in lap and shoulder belt webbing length of 276 and 258 mm, respectively. Gender did not have important effects on the analyzed belt fit measures after taking into account stature and body mass index. These results offer important considerations for future crash safety assessments and suggest that further research is needed to consider belt fit for older and obese occupants.