1999 proved to be another successful year for both the Acid Rain Program's rate-based approach to NOX reduction and cap-and-trade approach to SO2 reduction. In 1999, all Phase I affected utility units not only met their compliance goals, but exceeded them, achieving an overall reduction of 423,857 tons of NOX from 1990 levels, and maintaining the extraordinary reductions of more than 5 million tons of SO2 from 1980 levels, first achieved in 1995. Additionally, the 274 Phase II NOx early election units had increased emissions of two percent since 1990, while their utilization increased by 28 percent during the same period. Exceedance of compliance goals translates into additional environmental and health benefits. For example, the greater and earlier reductions of SO2 have resulted in a 10 - 25 percent drop in rainfall acidity in the Northeast in 1995 through 1997 since the beginning of Phase I. One factor mitigating the benefit of the over compliance in the SO2 program, of course, is the ability to use banked allowances in the future. The 40 percent of 1995 allowances, 35 percent of 1996 allowances, 23 percent of 1997 allowances, 24 percent of 1998 allowances, and 29 percent of 1999 allowances that were not retired for compliance purposes can be used to cover emissions in a later year. However, receiving health and environmental benefits earlier may be of greater value than receiving those benefits several years from now.