This data is from the U.S. Census Bureau’s “Annual State Survey of Government Finances” which gives the state governments’ expenditures for each function the government performs. Highways expenditures include two expenditure groups, regular highways and toll highways (Methodology for Summary Tabulations). The regular highways expenditures group applies to maintenance, operation, repair, and construction of highways, streets, and any public road way. The toll highways expenditures consists of maintenance, operation, repair, and construction of any highway, road, or ferry operated on a fee or toll basis. For more information on what each group includes see the U.S. Bureau of the Census Government Finance and Employment Classification Manual (Ch. 5, pp. 43-44).
Highways expenditures refers to the total amount spent by the state on highways given in billions.
The highways expenditures percentage is calculated as the amount spent on highways divided by total government expenditures. Highways expenditures per capita is calculated as the amount spent on highways divided by the state population in the given year.
According to the U.S. Census Bureau, “Expenditures comprise all amounts of money paid out by a government during its fiscal year, with some exceptions. Statistics on state government finance include measurement of expenditures by character (e.g., current operations, capital outlay, intergovernmental expenditures, and so on) and function (e.g., education, health, public welfare, natural resources, and so on). Expenditure does not include a government's payment of its debt, or purchases of investment securities, loans it has granted, agency or private trust transactions, nor correcting transactions” (State Government Finances Methodology).