U.S. domestic air cargo traffic took a sudden, steep turn downward in March, falling 5.5 percent in the largest decline in the business in nearly four years, according to the Air Transport Association.

The drop coincided with a rapid expansion in jet fuel prices, adding to airline industry concerns that shippers are moving goods over to surface transport to avoid the sharp escalation in fuel costs.

Overall cargo traffic for U.S. carriers fell 1 percent in March, the first decline since last June. International cargo edged up 2.7 percent, a figure that included just a 0.5 percent increase over last year in Atlantic air trade, the worst showing in that market since May 2005.

Domestic air cargo had been edging back up after a long period of stagnant volume, but the decline in March compared to the same month last year marked the first drop since last September and the largest slide in traffic within the United States since May 2005.

Express carriers UPS and FedEx recently issued warnings about slowing traffic in the United States and several passenger airlines have reported large declines in their monthly traffic reports. American Airlines said its cargo traffic fell 8.6 percent in March and 3.6 percent in April, although the airline does not separate out its domestic and international business in public reports.