An increase in FedEx Corp.’s overnight box shipments in the United States reinforces the Federal Reserve’s view that the economic expansion is on a “firmer footing,” Bloomberg reported.

Average daily volume rose 2.4 percent to 1.22 million boxes in the quarter ended Feb. 28 from a year earlier, the second-largest U.S. package-shipping company reported today. It was the highest level of such shipments for a fiscal third quarter since 2006.

“FedEx’s overnight box volume is one of the most reliable indicators of the state of the economy,” said Charles Clowdis, managing director of transportation advisory services at IHS Global Insight, a forecasting firm in Lexington, Mass. “Increased volumes certainly validate a steady recovery.”

Goods moved by Memphis-based FedEx account for at least 5 percent of the U.S. gross domestic product, with box shipments reflecting everything from auto parts to consumer purchases over the Internet, said Kevin Sterling, an analyst in Richmond, Va., at BB&T Capital Markets.