By the late 1960s, independent firms were supplying crash test dummies to automobile manufacturers, who had to prove that they were in compliance with federal seat belt standards. Dummies were fitted with internal sensing devices that measured and recorded impact. General Motors was not satisfied with dummies placed on the market, and in 1972 GM designed the Hybrid II, so named because it combined the best features of Alderson VIP and Sierra dummies with some original GM component designs. Unlike previous dummies, Hybrid II provided consistent results under similar conditions. Hybrid II also had a human-like slouch, a rubber neck instead of ball-and-socket, and well defined knee-leg action. GM shared its design with competitors and dummy manufacturers. In 1973, the National Highway Traffic Safety Administration certified Hybrid II as the only dummy approved for seat belt compliance testing.
In the 1970s, General Motors began developing the more sophisticated Hybrid III, a sensitive, humanlike dummy that simulated and measured injuries to many parts of the body. Hybrid III had a better defined head, neck, spine, and posture than Hybrid II, and its 41 channels of information (compared to 8 channels in Hybrid II) measured impact to the head, torso, knee, and leg with greater precision. In 1997 the National Highway Traffic Safety Administration recognized Hybrid III as the only dummy to be used for compliance testing.