Greenhouse gas (GHG) regulation started with the 2011 EPA/DOT release, sometimes termed as GHG Phase 1. One foundation of this regulation was that it applied only to new vehicles built by larger OEMs who would need to balance their annual production mix of compliant vehicles with non-compliant ones so their annual production averages overall would meet the standards.
The pain of compliance was then squarely on the OEMs. That is changing.
