Comment by millstone

CA is large but circa ~10% of national truck sales. 10% is no monopoly - hell the Texas truck market is at least twice the size of CA.

What's missing is the fact that 12 other states (the west coast and most of New England) have voluntarily agreed to adopt California's standards. So yes, the rest of the country does have influence, and they're wielding that influence on California's side.

Nobody is being "forced" to comply. Instead CA's standards are reasonable enough that it's more economical to implement them nationally than to build two models.