All SIPs show continued reductions in mobile source emissions, at least through 2010. Conformity failure simply means that mobile sector emissions are not projected to decline quite as fast as the state SIP says they should. These projections, of course, are based on models whose uncertainties could overwhelm any projected emissions difference. The other problem is that states make a political decision and set the mobile source emissions budget too tight. To lessen the emissions reduction burden on stationary sources, which, by the way, have not reduced their overall emissions since 1970 to the same extent the mobile sector has.
Conformity needs to be redefined.
Federal conformity requirements are forcing state and local governments to go through long and costly modeling exercises that are based on nothing more than guesses. No one knows with any degree of certainty what national, state and local economies will be 12 to 20 years from now. We can guess, but we don't know. We can guess, but we don't know, what a state or region's demographics will look like in 2020. Compounding the problem, the models don't account for new, cleaner automotive and motor fuel technologies that we know are on the horizon and are going to have a major impact on future mobile source emissions.