A new report from the National Research Council examines major policies that could save energy and reduce emissions from the U.S. transportation sector over the next 20 to 50 years. It will take more than tougher fuel economy standards for U.S. transportation to significantly cut its oil use over the next half century.  It will likely require a combination of measures that foster consumer and supplier interest in vehicle fuel economy, alternative fuels, and a more efficient transportation system, says a new report from the National Research Council.  Public interest in reducing the cost of securing the nation's energy supplies, curbing emissions of carbon dioxide and other greenhouse gases (GHGs), and improving transportation operations could motivate such varied actions. "It is not simply a matter of choosing a single best policy," said Emil Frankel, director of transportation policy, Bipartisan Policy Center, Washington, D.C., and chair of the committee that wrote the report.  "Decisions about whether and how to reduce transportation's use of oil will require officials to consider a range of options." The U.S. transportation sector accounts for more than two-thirds of the nation's oil use and about 25 percent of its carbon dioxide emissions.  Federal regulations over the past [...]