Like virtually every other industry, US railroads took a big hit following the onset of the recession in late 2008. But they had learned a lesson from the earlier slump in 2001, and rather than eviscerating spending, this time the railroads invested in capital improvements that would prepare them for the time that the economy picked up.

So far this year, their prescience has been rewarded with 7.2% growth in freight volume. In May alone, freight carloads totaled 1.15 million cars, up nearly 16% from the May 2009. Union Pacific (NYSE: UNP), the country’s largest railroad, showed a volume gain of 13%, with shipments of cars and car parts up a whopping 75%.

In February, Berkshire Hathaway Inc. (NYSE: BRK-A) completed its purchase of Burlington Northern Santa Fe, which investing icon Warren Buffet said was “an all-in wager on the economic future of the United States.” BNSF cost Buffett $34 billion, his most expensive acquisition ever.

All the railroad signs to this point indicate that Buffett could be right and that the economy is improving. Other railroads, like CSX Corp. (NYSE: CSX), Norfolk Southern Corp. (NYSE: NSC), Canadian National Railway Co. (NYSE: CNI), and Canadian Pacific Railway Ltd. (NYSE:CP), have not said much about their prospects for the rest of the year, but figures from the Association of American Railroads point to better days ahead.

The largest volume commodity transported by rail is coal, amounting to nearly 44% of all freight. Coal carloads increased 6.8% in May 2010 compared with a year ago. Agricultural and food products, which account for about 13% of volume, rose 8% year-over-year. May ore shipments, primarily iron ore, are up a stupendous 120% over May 2009.

Another big gainer was the intermodal category, which includes trailers and shipping containers that can be moved either by truck or ship as well as rail. Intermodal volume grew by 18.9%, with containers up by more than 20%. Because containers typically originate in foreign countries, the rise in volume indicates a greater demand for goods, which in turn indicates consumers who are willing to spend.

But all these indicators and the good news in general about railroad shipments is belied by the fact that the US economy just doesn’t seem to be on even a slow and steady growth path. One possibility is that projected rail shipments are lagging indicators of economic strength. Another possibility is that railroad executives are looking at the same glass as the rest of us, but they see it as half full and getting fuller.

The railroad industry still has a long ways to go to reach 2008 volume. Coal volumes remain more than 10% below 2008 levels, autos and auto parts are 23.7% lower, and forest products are 25.5% lower.

Lumber and wood product shipments are more than 30% below 2008 levels. This is just one more sign that a recovery in the housing industry is not likely in the near term.

To put the best face on it, the railroaders are positioned to spur a US economic recovery as soon as that recovery shows up.