The last week in March is great for statistics. Corporate types put the final touches on the blizzard of numbers they release in annual reports. Basketball fans look at their busted brackets and wonder how those teams could have made the Final Four. Stat-obsessed baseball fans are hurriedly prepping for opening day.

Business travelers? We have the annual data dump from the Bureau of Transportation Statistics (BTS). It arrived in a neat little bundle on Monday, complete with charts and percentages and some important revelations about the condition of our condition on the road.

So let's tiptoe through the data tables and try to figure out what it all means.

Let's Get Small(er)

The nation's air-transportation system continues to contract. Including domestic and international itineraries, 769.6 million people flew last year. That's 5.3 percent less than 2008's 812.3 million and more than 8 percent below 2007's total of 838.2 million. The decline covered both domestic (down 5.2 percent) and international (down 6.3 percent) travel. The decrease was also a yearlong reality; the passenger count declined in 10 months last year compared to the same month in 2008. The fall was most pronounced in the first half of last year, however. Travel fell 9 percent in the first six months of 2009. It was off a more modest 1.4 percent in the last six months. Of course, travel plummeted late in 2008 after Merrill Lynch tanked, so the comparison is a bit skewed.

The New Powerhouse in the Skies

Southwest Airlines' keep-it-simple-stupid approach to air travel—it offers the same service, the same seats, and the same fare structure on every flight on every day on every route across its system—rules the skies. For the third consecutive year, Southwest carried more passengers than any other U.S. carrier. It was the only airline to carry more than 100 million passengers in 2009, and it even flew more travelers than No. 4 United Airlines (56 million passengers in 2009) and No. 6 Continental Airlines (43 million) combined. This is all the more astounding when you consider that Southwest doesn't fly overseas. American Airlines is the largest U.S. carrier with international service. It carried a total of 85.7 million passengers; 19.5 million of them flew internationally.

One Plus One Equals Less Than Two

The BTS statistics reported separately for Delta Air Lines and Northwest Airlines even though the two carriers were joined at the corporate hip for most of 2009 and officially merged on December 31. Taken together, they carried 108.5 million passengers. That would have made it slightly larger than Southwest, which carried 101.3 million customers. (Delta-Northwest's combined total of 20.4 million international passengers would have made it slightly larger than American's overseas traffic too.) But the numbers are deceiving because Delta is shrinking fast. In 2008, Delta and Northwest carried a combined total of 120.3 million passengers. That means the two carriers in 2009 shrank almost 10 percent compared to 2008.

We're No. 10!

The nation's 10th-largest carrier in terms of passengers carried? SkyWest Airlines, which enplaned 21.4 million customers in 2009. Never heard of SkyWest? No surprise, really. It's a "regional carrier": industry jargon for a commuter operator that flies almost totally under some other carrier's brand name. All but a handful of SkyWest's 1,748 daily departures are operated as United Express (for United) or Delta Connection (for Delta). SkyWest's growth is emblematic of the industry's obsession with handing off service to subcontractors who fly smaller planes and pay their employees less. In fact, regional carriers like SkyWest now operate about half of the nation's flights and carry one in five domestic travelers.