Add one more indicator to the list showing that the Minnesota economy is struggling to build momentum: travel.

The number of people who flew out of Minneapolis-St. Paul International Airport fell in May compared with a year ago, according to new figures from the airport. About 2.7 million people boarded flights in the month, a 1.5 percent decline from the same month a year ago.

Consumers and businesses who fly demonstrate confidence in the economy, and they spend money on airfare, hotels, car rentals, and restaurant meals.

So far this year, the number of people flying out of Minnesota's largest airport has risen slightly. The data has roughly tracked the trajectory of jobs numbers in the state, as February and March were strong, followed by weaker numbers in April and May.

Air travel was hurt by the April spike in fuel prices, said David Levinson, a professor at the University of Minnesota's Center for Transportation Studies.

"The price of fuel is certainly very volatile, and that doesn't necessarily say something about the broader economy," Levinson said. "The sensitivity of enplanements is in part due to the airfares that are charged."

But as of the end of 2011, annual air travel out of the Twin Cities still was 11 percent below 2005.

The biggest growth in air travel in the Upper Midwest is happening near the oil fields in northwest North Dakota, according to data collected by the Federal Reserve Bank of Minneapolis.

Airports in North Dakota, South Dakota and Montana have gotten busier since 2007. Airports in Minnesota and Wisconsin lost business over the same four years.

Meanwhile, vehicle miles driven fell across the nation slightly in April, hurt by a spike in gasoline prices, the U.S. Department of Transportation reported.

Adam Belz • 612-673-4405