According to a recent study carried out by the Rocky Mountain Institute, the United States could cut their consumption of coal by 62 % before as early as 2020. This would represent savings of 1.2m gigawatt-hours annually.
The equivalent of 30 % of the US annual electricity use could be saved by increasing the energy efficiency of the 40 least energy efficient States to the levels of the 10 most efficient.
This could be achieved only by improving the productivity of the local electricity networks. For further details, please check out this article from Business Green.