The 1990 CAA strengthened conformity requirements that require metropolitan planning organizations in non-attainment and maintenance areas to use the most recent mobile source emission estimate models to show that (a) all federally funded and "regionally significant projects," including non-federal projects in regional transportation improvement programs (TIPs) and plans will not lead to emissions higher than those in the 1990 baseline year, and (2) by emarking on these projects, emissions will be lower than in the no-build scenario