WASHINGTON (AP) — The outgoing secretary of transportation says stimulating private investment in infrastructure projects, as Donald Trump has proposed, can cover only a fraction of the costs of solving America's transportation problems.

Anthony Foxx tells The Associated Press that "a fair amount of public funding" will still be needed. He said public private partnerships involving both government money and private capital could pay for only about 10 percent to 20 percent of the costs.

Such partnerships typically rely on revenue from tolls or other revenue to provide investors with a profit, and have had a mixed record of success.

The president-elect has promised to generate $1 trillion in transportation and other infrastructure spending, putting people to work in the process.