ISO 16121-1, ISO 18375, and ISO 26262 These a some of the standards required to build a new bus You are correct Thailand does not build New busses they build on old chassis and there are NO standards for this, the standards and testing required to meet iso standards Thailand can not meet, cost to much, its easy to build on old chassis no standards to meet use any materials that is one of the reason busses burn here good, Thailand has these standards but no enforcement, remember safety costs money live are cheap