The public and private sectors in the United States together spend over $500 billion a year on infrastructure projects, including highways and airports, water and energy utilities, dams, waste disposal sites and other environmental facilities, schools, and hospitals. The federal government makes a significant contribution to that investment through its direct expenditures and the subsidies it provides indirectly through the tax system, which are sometimes referred to as tax expenditures. CBO and the Joint Committee on Taxation (JCT) have released a study on the importance of tax preferences, the types of tax-preferred bonds used in financing infrastructure, and the economic efficiency of such bonds. That study concludes that the amount that the federal government forgoes through tax-exempt bond financing is greater than the associated reduction in borrowing costs for state and local governments. Some analysts have estimated the magnitude of that differential and conclude that several billion dollars each year may simply accrue to bondholders in higher income-tax brackets without providing any cost savings to borrowers.