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The Tax Policy Center's

Briefing Book

A citizen’s guide to the fascinating (though often complex) elements of the US tax system.

Tax Policy Center Briefing Book

Key Elements of the U.S. Tax System

  • Briefing Book
  • Excise Taxes
  • What is the Highway Trust Fund, and how is it financed?
  • Chapters
    • Introduction
      • Introduction
        • Introduction
    • Some Background
      • Federal Budget
        • What are the sources of revenue for the federal government?
        • How does the federal government spend its money?
        • What is the breakdown of revenues among federal, state, and local governments?
        • How do US taxes compare internationally?
      • Federal Budget Process
        • How does the federal budget process work?
        • What is the history of the federal budget process?
        • What is the schedule for the federal budget process?
        • What is reconciliation?
        • How is a budget resolution enforced?
        • What is PAYGO?
        • What are rescissions?
      • Federal Budget Outlook
        • How accurate are long-run budget projections?
        • What have budget trends been over the short and long term?
        • How much spending is uncontrollable?
        • What are tax extenders?
        • What options would increase federal revenues?
        • What does it mean for a government program to be off-budget?
        • How did the TCJA affect the federal budget outlook?
      • Taxes and the Economy
        • How do taxes affect the economy in the short run?
        • How do taxes affect the economy in the long run?
        • What are dynamic scoring and dynamic analysis?
        • Do tax cuts pay for themselves?
        • On what do economists agree and disagree about the effects of taxes on economic growth?
        • What are the economic effects of the Tax Cuts and Jobs Act?
      • Economic Stimulus
        • What is the role of monetary policy in alleviating economic downturns?
        • What are automatic stabilizers and how do they work?
        • What characteristics make fiscal stimulus most effective?
      • Distribution of Tax Burdens
        • How are federal taxes distributed?
        • Are federal taxes progressive?
        • How should progressivity be measured?
        • What is the difference between marginal and average tax rates?
        • What criticisms are levied against standard distributional analysis?
        • How should distributional tables be interpreted?
        • Who bears the burden of the corporate income tax?
        • Who bears the burden of federal excise taxes?
        • How do financing methods affect the distributional analyses of tax cuts?
        • How do taxes affect income inequality?
      • Tax Expenditures
        • What are tax expenditures and how are they structured?
        • What is the tax expenditure budget?
        • Why are tax expenditures controversial?
        • What are the largest tax expenditures?
        • How did the TCJA affect tax expenditures?
      • Tax Gap and Tax Shelters
        • What is the tax gap?
        • What does the IRS do and how can it be improved?
        • What is a tax shelter?
      • Recent History of the Tax Code
        • What did the 2008–10 tax stimulus acts do?
        • What did the American Taxpayer Relief Act of 2012 do?
        • How did the Tax Cuts and Jobs Act change personal taxes?
        • How did the Tax Cuts and Jobs Act change business taxes?
    • Key Elements of the U.S. Tax System
      • Individual Income Tax
        • What is the standard deduction?
        • What are itemized deductions and who claims them?
        • How did the TCJA change the standard deduction and itemized deductions?
        • What are personal exemptions?
        • How do federal income tax rates work?
        • What are tax credits and how do they differ from tax deductions?
        • How do phaseouts of tax provisions affect taxpayers?
      • Capital Gains and Dividends
        • How are capital gains taxed?
        • What is the effect of a lower tax rate for capital gains?
        • What is carried interest, and how is it taxed?
        • How might the taxation of capital gains be improved?
      • AMT
        • What is the AMT?
        • Who pays the AMT?
        • How much revenue does the AMT raise?
        • How did the TCJA change the AMT?
      • Taxes and the Family
        • What is the child tax credit?
        • What is the adoption tax credit?
        • What is the earned income tax credit?
        • Do all people eligible for the EITC participate?
        • How does the tax system subsidize child care expenses?
        • What are marriage penalties and bonuses?
        • How did the TCJA change taxes of families with children?
      • Taxes and the Poor
        • How does the federal tax system affect low-income households?
        • What is the difference between refundable and nonrefundable credits?
        • Can poor families benefit from the child tax credit?
        • Why do low-income families use tax preparers?
        • How does the earned income tax credit affect poor families?
        • What are error rates for refundable credits and what causes them?
        • How do IRS audits affect low-income families?
      • Taxes and Retirement Saving
        • What kinds of tax-favored retirement arrangements are there?
        • How large are the tax expenditures for retirement saving?
        • What are defined benefit retirement plans?
        • What are defined contribution retirement plans?
        • What types of nonemployer-sponsored retirement savings accounts are available?
        • What are Roth individual retirement accounts?
        • Who uses individual retirement accounts?
        • How does the availability of tax-favored retirement saving affect national saving?
        • What’s the difference between front-loaded and back-loaded retirement accounts?
        • What is an automatic 401(k)?
        • How might low- and middle-income households be encouraged to save?
      • Taxes and Charitable Giving
        • What is the tax treatment of charitable contributions?
        • What entities are tax-exempt?
        • Who benefits from the deduction for charitable contributions?
        • How would various proposals affect incentives for charitable giving?
        • How large are individual income tax incentives for charitable giving?
        • How did the TCJA affect incentives for charitable giving?
      • Taxes and Health Care
        • How much does the federal government spend on health care?
        • Who has health insurance coverage?
        • Which tax provisions subsidize the cost of health care?
        • How does the tax exclusion for employer-sponsored health insurance work?
        • What are premium tax credits?
        • What tax changes did the Affordable Care Act make?
        • How do health savings accounts work?
        • How do flexible spending accounts for health care expenses work?
        • What are health reimbursement arrangements and how do they work?
        • How might the tax exclusion for employer-sponsored health insurance (ESI) be reformed?
      • Taxes and Homeownership
        • What are the tax benefits of homeownership?
        • Do existing tax incentives increase homeownership?
      • Taxes and Education
        • What tax incentives exist for higher education?
        • What tax incentives exist to help families pay for college?
        • What tax incentives exist to help families save for education expenses?
        • What is the tax treatment of college and university endowments?
      • Tax Complexity
        • Why are taxes so complicated?
        • What are the benefits of simpler taxes?
        • What policy reforms could simplify the tax code?
      • Wealth Transfer Taxes
        • How do the estate, gift, and generation-skipping transfer taxes work?
        • Who pays the estate tax?
        • How many people pay the estate tax?
        • What is the difference between carryover basis and a step-up in basis?
        • How could we reform the estate tax?
        • What are the options for taxing wealth transfers?
        • What is an inheritance tax?
      • Payroll Taxes
        • What are the major federal payroll taxes, and how much money do they raise?
        • What is the unemployment insurance trust fund, and how is it financed?
        • What are the Social Security trust funds, and how are they financed?
        • Are the Social Security trust funds real?
        • What is the Medicare trust fund, and how is it financed?
      • Excise Taxes
        • What are the major federal excise taxes, and how much money do they raise?
        • What is the Highway Trust Fund, and how is it financed?
      • Energy and Environmental Taxes
        • What tax incentives encourage energy production from fossil fuels?
        • What tax incentives encourage alternatives to fossil fuels?
        • What is a carbon tax?
      • Business Taxes
        • How does the corporate income tax work?
        • What are pass-through businesses?
        • How are pass-through businesses taxed?
        • Is corporate income double-taxed?
      • Tax Incentives for Economic Development
        • What is the new markets tax credit, and how does it work?
        • What is the Low-Income Housing Tax Credit and how does it work?
        • What are Opportunity Zones and how do they work?
      • Taxes and Multinational Corporations
        • How does the current system of international taxation work?
        • How do US corporate income tax rates and revenues compare with other countries’?
        • What are the consequences of the new US international tax system?
        • How does the tax system affect US competitiveness?
        • How would formulary apportionment work?
        • What are inversions, and how will TCJA affect them?
        • What is a territorial tax and does the United States have one now?
        • What is the TCJA repatriation tax and how does it work?
        • What is the TCJA base erosion and anti-abuse tax and how does it work?
        • What is global intangible low-taxed income and how is it taxed under the TCJA?
        • What is foreign-derived intangible income and how is it taxed under the TCJA?
    • How Could We Improve the Federal Tax System?
      • Comprehensive Tax Reform
        • What is comprehensive tax reform?
        • What are the major options for comprehensive tax reform?
      • Broad-Based Income Tax
        • What is a broad-based income tax?
        • What would and would not be taxed under a broad-based income tax?
        • What would the tax rate be under a broad-based income tax?
      • National Retail Sales Tax
        • What is a national retail sales tax?
        • What would and would not be taxed under a national retail sales tax?
        • What would the tax rate be under a national retail sales tax?
        • What is the difference between a tax-exclusive and tax-inclusive sales tax rate?
        • Who bears the burden of a national retail sales tax?
        • Would tax evasion and avoidance be a significant problem for a national retail sales tax?
        • What would be the effect of a national retail sales tax on economic growth?
        • What transition rules would be needed for a national retail sales tax?
        • Would a national retail sales tax simplify the tax code?
        • What can state and local sales taxes tell us about a national retail sales tax?
        • What is the experience of other countries with national retail sales taxes?
        • What did the President’s Advisory Panel on Federal Tax Reform say about the national retail sales tax?
      • Value Added Tax (VAT)
        • What is a VAT?
        • How would a VAT be collected?
        • What would and would not be taxed under a VAT?
        • What would the tax rate be under a VAT?
        • What is the difference between zero rating and exempting a good in the VAT?
        • Who would bear the burden of a VAT?
        • Is the VAT a money machine?
        • How would small businesses be treated under a VAT?
        • What is the Canadian experience with a VAT?
        • Why is the VAT administratively superior to a retail sales tax?
        • What is the history of the VAT?
        • How are different consumption taxes related?
      • Other Comprehensive Tax Reforms
        • What is the flat tax?
        • What is the X-tax?
      • Recent Comprehensive Tax Reform Proposals
        • Simple, Fair, and Pro-Growth: Proposals to Fix America’s Tax System, Report of the President’s Advisory Panel on Federal Tax Reform, November 2005
        • The Moment of Truth: Report of the National Commission on Fiscal Responsibility and Reform, December 2010
        • Debt Reduction Task Force, “Restoring America’s Future,” Bipartisan Policy Center, November 2010
        • The Tax Reform Act of 2014: Fixing Our Broken Tax Code So That It Works for American Families and Job Creators, House Ways and Means Committee
        • The Graetz Competitive Tax Plan, Updated for 2015
      • Return-Free Tax Filing
        • What is return-free filing and how would it work?
        • What are the benefits of return-free filing?
        • What are the drawbacks of return-free filing?
        • How would the tax system need to change with return-free filing?
        • Who would qualify for return-free filing?
        • Would return-free filing raise taxes?
        • What was the experience with return-free filing in California?
        • What other countries use return-free filing?
    • The State of State (and Local) Tax Policy
      • State and Local Revenues
        • What are the sources of revenue for state governments?
        • What are the sources of revenue for local governments?
      • Specific State and Local Taxes
        • How do state and local individual income taxes work?
        • How do state and local sales taxes work?
        • How do state and local property taxes work?
        • How do state and local corporate income taxes work?
        • How do state estate and inheritance taxes work?
        • How do state earned income tax credits work?
        • How do state and local severance taxes work?
        • How do state and local soda taxes work?
        • How do marijuana taxes work?
      • Fiscal Federalism and Fiscal Institutions
        • How does the deduction for state and local taxes work?
        • What are municipal bonds and how are they used?
        • What types of federal grants are made to state and local governments and how do they work?
        • What are state rainy day funds, and how do they work?
        • What are tax and expenditure limits?
        • What are state balanced budget requirements and how do they work?
    • Glossary
      • Glossary
        • Glossary

What is the Highway Trust Fund, and how is it financed?

Excise Taxes

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Federal Budget and Economy
Q.

What is the Highway Trust Fund, and how is it financed?

A.

The Highway Trust Fund finances most federal government spending for highways and mass transit. Revenues for the trust fund come from transportation-related excise taxes, primarily federal taxes on gasoline and diesel fuel. In recent years, however, the trust fund has needed significant transfers of general revenues to remain solvent.

The Highway Trust Fund tracks federal spending and revenue for surface transportation. The trust fund has separate accounts for highways and mass transit. Because obligations from the trust fund generally are for capital projects that take several years to complete, outlays reflect projects authorized by Congress in previous years.

Most spending from the Highway Trust Fund for highway and mass transit programs is through federal grants to state and local governments. The federal government accounts for about one-quarter of all public spending on roads and highways, with the remaining three-quarters financed by state and local governments.

Financing the Trust Fund

The Congressional Budget Office estimates that Highway Trust Fund tax revenue will total $43 billion in fiscal year 2020 (figure 1). Revenue from the federal excise tax on gasoline ($25.8 billion) and diesel fuel ($10.5 billion) accounts for 84 percent of the total. The remaining trust fund tax revenue comes from a sales tax on tractors and heavy trucks, an excise tax on tires for heavy vehicles, and an annual use tax on those vehicles. In addition to dedicated tax revenue, the trust fund receives a small amount of interest on trust fund reserves.

The current tax rates are 18.4 cents per gallon for gasoline and ethanol-blended fuels and 24.4 cents per gallon for diesel (0.1 cent of each tax is dedicated to the Leaking Underground Storage Tank Trust Fund). The tax rates on motor fuels have not changed since 1993 and thus have failed to keep pace with inflation. If tax rates had been indexed for inflation since 1993, the current tax on gasoline would be about 33 cents per gallon and the tax on diesel fuel would be about 44 cents per gallon. Although the current taxes on motor fuels (except for a residual tax of 4.3 cents per gallon) are set to expire at the end of September 2022, Congress has routinely extended the taxes in the past.

Trust Fund Balances

Before 2008, highway tax revenue dedicated to the trust fund was sufficient to pay for outlays from the fund, but that has not been true in recent years. Since 2008, Congress has sustained highway spending by transferring over $140 billion of general revenues to the fund, including $70 billion in the Fixing America’s Surface Transportation Act in 2015.

Those transfers will enable the trust fund to meet spending obligations through 2020, but projected shortfalls will appear again by the end of 2021 (figure 2). The Congressional Budget Office projects that, by 2030, outlays from the Highway Trust Fund will exceed trust fund reserves by a cumulative $134 billion for the highway account and by $54 billion for the mass transit account, even if expiring trust funds taxes are extended (Congressional Budget Office 2020).

Financing Federal Spending on Highways and Mass Transit

Congress could pay for projected highway and mass transit spending by simply raising the federal tax rate on gasoline and diesel fuel. A one cent increase in motor fuels taxes dedicated to the Highway Trust Fund would raise trust fund revenues by between $1.5 billion and $1.7 billion annually (Kile 2015). (Higher motor fuels taxes would increase costs for businesses, thus lowering business profits, employee wages, and the federal taxes collected on that income. The estimated increase in Highway Trust Fund revenues does not include the reduction in federal revenues from other sources.)

Drivers likely would respond to an increase in motor fuels taxes by driving less, which would reduce pollution and lessen the need for highway construction and maintenance. But drivers may also respond by driving more fuel-efficient vehicles, which would weaken the incentive to reduce miles driven.

Motor fuels taxes link highway use with the associated costs of building and maintaining roads as well other costs associated with fuel consumption, such as pollution and dependence on foreign oil. But motor fuels taxes are an imperfect user fee because they do not differentiate among vehicles that cause greater or lesser road wear for the same amount of fuel consumed or between travel on crowded and uncrowded roads.

A tax on vehicle miles driven would provide a more direct link to the cost of highway use but, unlike an increase in the tax on motor fuels, would be difficult to implement, requiring new tolls or electronic motoring of vehicles. An advantage of a vehicle mileage tax is that it could adjust to reflect the additional costs of congestion by increasing tolls or the tax rate in certain locations and at certain times of the day. A vehicle mileage tax would not, however, provide an incentive for driving more fuel-efficient vehicles.

Alternatively, Congress could abandon the user-pay principle and simply pay for highways through general revenues. Highway spending would no longer have a dedicated source of revenue and would instead compete with other spending programs for general revenue funding through the annual appropriations process. Or Congress could decide to limit federal highway spending to the amount of revenue collected from exiting motor fuels taxes. This would require curtailing some existing highway projects and not starting others, at a time when the nation’s infrastructure is already in need of repair.

Updated May 2020
Data Sources

Congressional Budget Office. 2020. The Budget and Economic Outlook: 2020 to 2030. Washington, DC: Congressional Budget Office.

Further Reading

Congressional Budget Office. 2014. “The Highway Trust Fund and the Treatment of Surface Transportation Programs in the Federal Budget.” Washington, DC: Congressional Budget Office.

Joint Committee on Taxation. 2015. “Long-Term Financing of the Highway Trust Fund.” JCX-92-15. Washington, DC: Joint Committee on Taxation.

Kile, Joseph. 2015. “Testimony on the Status of the Highway Trust Fund and Options for Paying for Highway Spending.” Testimony before the US Senate Committee on Finance, Washington, DC, June 18.

Kirk, Robert S. and William J. Mallet. 2019 “Funding and Financing Highways and Public Transportation.” R45350. Washington, DC: Congressional Research Service. Updated June 7, 2019

Peter G. Peterson Foundation. 2018. “The Highway Trust Fund Explained.” Washington, DC: Peter G. Peterson Foundation. June 27.

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