Ford had infants and seniors in mind when it designed the 2011 Ford Explorer to have rear seat belts that include small built-in airbags. The inflatable belts, which will be optional on the Explorer, are devised to reduce head, neck and chest injuries in young children and the elderly. Ford safety officials said infants and seniors are the passengers most likely to ride in the back seat and most susceptible to injuries in a crash. The Explorer is switching from a truck-based body-on-frame platform to a unibody or one-piece body and chassis.