An anthropomorphic test device includes a pelvis member. The pelvis member has a foam core and includes an abdomen region defining a first cavity and a pair of thigh regions extending from the abdomen region. The pelvis member also includes a buttock region positioned below the abdomen region and rearward of the pair of thigh regions. The buttock region defines a buttock cavity separate from the first cavity with the buttock region also defining at least one vent port. The buttock cavity compresses from an open condition to a collapsed condition when the anthropomorphic test device is placed onto a surface for approximating a force applied by a body weight of a human.