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 20g deceleration and an impact by an unrestrained occupant to the rear. In the United States, NHTSA has now required lap-shoulder seat belts in new "over-the-road" buses (includes most coaches) starting in 2016. The use of seatbelts in trains has been investigated. Concerns about survival space intrusion in train crashes and increased injuries to unrestrained or incorrectly restrained passengers led the researchers to discourage the use of seat belts in trains. Lap belts are found on all passenger aircraft. Many civil aviation authorities require a "fasten seat belt" sign in passenger aircraft that can be activated by a pilot during