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Seat comfort is driven in part by the fit between the sitter and seat. Traditional anthropometric data provide little information about the size and shape of the torso that can be used for backrest design. This study introduces a methodology for using three-dimensional computer models of the human torso based on a statistical analysis of body shapes for conducting automated fit assessments. Surface scan data from 296 men and 417 women in a seated posture were analyzed to create a body shape model that can be adjusted to a range of statures, body shape, and postures spanning those typical of vehicle occupants. Finite-element models of two auto seat surface were created, along with custom software that generates body models and postures them in the seat. A simple simulation technique was developed to rapidly assess the fit of the torso relative to the seat back.

The effects of seatbelt use, muscle tension, lower-extremity posture, driver fore-aft seat position, seat height, and seat angle on the likelihood of knee, thigh, and hip (KTH) injuries during knee-to-knee-bolster impacts in frontal crashes were studied using a finite element (FE) human model. A midsize male whole-body FE model, with a previously validated knee-impact response, was further validated in this study against whole-body responses from two sets of cadaver sled tests. This human model was integrated with vehicle instrument panel, seat, and restraint-system models. An FMVSS 208 crash pulse of a passenger car was used to evaluate the effects of the aforementioned factors on the risk of KTH injuries. Simulation results indicated that seatbelts significantly reduced peak forces generated at the knee, in the thigh, and at the hip, and thereby reduced the risk of KTH injuries.