"The authorization for federal spending on highway and public transportation programs, as well as surface transportation safety and research and some rail programs, expires September 30, 2014. The existing authorization, the Moving Ahead for Progress in the 21st Century Act (MAP-21; P.L. 112-141) was a two-year bill, funding FY2013 and FY2014. Nearly all the funding for highways and most of the funding for public transportation is drawn from the highway trust fund (HTF). However, the motor fuel taxes that are the main source of HTF revenue no longer raise enough money to support the programs Congress has authorized. Congressional Budget Office projections indicate that the shortfall between revenues and outlays will average roughly $15 billion annually from FY2015 through FY2020. MAP-21 made up the most of the difference between motor fuel tax revenue and spending authorization by transferring money from the Treasury general fund to the HTF. As Congress considers surface transportation reauthorization, the funding shortfall is the major issue framing the debate. The alternatives will involve choices among raising motor fuels taxes, cutting spending, finding other revenue sources for the HTF, approving further transfers from the general fund, and seeking to increase private investment in surface transportation infrastructure. MAP-21 made major changes in the program structure for both highways and public transportation. Some of the changes were designed to increase program efficiency by requiring performance measurement and streamlining project development. As these changes are recent, their effectiveness may be difficult to evaluate."
CRS Report for Congress, R43420
The National Agricultural Law Center: http://www.nationalaglawcenter.org/