"The failure of federal highway user taxes and fees to provide sufficient revenues to support even baseline surface transportation spending levels has encouraged Congress to consider expanded toll financing. Congress has cautiously encouraged increased use of tolling in recent transportation legislation, including the Moving Ahead for Progress in the 21st Century Act (MAP-21; P.L. 112-141). Recent projections of a $15 billion annual gap between revenue anticipated from taxes dedicated to surface transportation and the cost of maintaining the current federal surface transportation program have stimulated interest in changing tolling policy in conjunction with reauthorizing or replacing MAP-21. Congress could achieve an expansion of tolling in several ways. At one extreme, it could simply encourage additional tolling pilot projects and a further expansion of tolling-supported innovative finance, such as more loans for road and bridge construction through the U.S. Department of Transportation's (DOT's) Transportation Infrastructure Finance and Innovation Act (TIFIA) program, which would be repaid through user tolls. At the other extreme, Congress might authorize states to toll federal-aid highways as they see fit, or even require that Interstate Highway segments be converted to toll roads as they undergo reconstruction in the future, eventually turning all Interstates into toll roads."
CRS Report for Congress, R43575