of Public Law 108–18. The law requires that savings attributable to the legislation after 2005 be held in escrow and not obligated or expended until otherwise provided for by law.

     The Postal Service measure of productivity, Total Factor Productivity (TFP), includes all factors of production. TFP measures the growth in the ratio of outputs and the inputs, or resources, expended in producing those outputs. By tracking outputs and resource usage, TFP provides a historical measure of efficiency.

     The Postal Service's main outputs are mail volumes and servicing an expanding delivery network. To account for variations in resources used to process different types of mail, TFP weights each mail type according to its workload content. The weighting is determined by factors such as size, weight, mailer preparation including barcoding and presorting, and mode of transportation used, such as air or highway. In addition to labor, TFP also measures capital and materials inputs, such as mechanized and automated equipment, facilities, transportation, and other nonpersonnel costs. The Output per Workhour component of TFP uses only labor input as a measure of resource use.