Across individuals, an increase in BMI of 10-kg/m2 was associated with a lap belt positioned 43 mm further forward and 21 mm higher relative to the pelvis.

Each 10-kg/m2 increase in BMI was associated with an increase in lap belt webbing length of 130 mm. The worsening of lap belt fit with restricted foot position was slightly greater for obese participants.

Obesity was associated with a more-inboard shoulder belt routing across a wide range of upper belt anchorage locations, and the shoulder belt webbing length between the D-ring and latchplate increased by an average  of 60 mm with each 10-kg/m2 increase in BMI.

The results suggest that obesity effectively introduces slack in the seat belt system by routing the belt further away from the skeleton. Particularly in frontal crashes, but also in rollovers and other scenarios, this slack may result in increased excursions and an increased likelihood and severity of contacts with the interior.

The higher routing of the lap belt with respect to the pelvis also may increase the likelihood of submarining in frontal crashes.