Seat belt that required a particular technical approach would rapidly become dated as motor manufacturers would tool up for a particular standard which could not easily be changed. For example, in 1969 there were competing designs for lap and three-point seat belts, rapidly tilting seats, and airbags being developed. But as countries started to mandate seat belt restraints the global auto industry invested in the tooling and standardized exclusively on seat belts, and ignored other restraint designs such as air bags for several decades As of 2016, seat belt laws can be divided into two categories: primary and secondary. A primary seat
Seat belt would defeat this system by fastening the seat belts with the seat empty and leaving them that way. To combat this dangerous habit, in 1971 NHTSA amended Federal Motor Vehicle Safety Standard № 208 (FMVSS 208) to require a seat belt/starter interlock system to prevent passenger cars from being started with an unbelted front-seat occupant. This mandate applied to passenger cars built after August 1973, i.e., starting with the 1974 model year. The specifications required the system to permit the car to be started only if the belt of an occupied seat were fastened after the occupant sat down, so