On shelves at a Humanetics facility in Huron, Ohio, skulls stare from their eyeless sockets, shiny and silver. Around a corner, a rack is filled with squishy, peach-toned arms, legs, torsos and butts.

The U.S. government announced major design changes it wants to implement to make the female version of the vehicle crash test dummy more lifelike, potentially replacing a model used for decades that ...