Although large railroad operators like Union Pacific (NYSE:UNP), Burlington Northern (NYSE:BNI), and CSX (NYSE:CSX) might be the names you see rolling by on your local tracks, investors shouldn't ignore smaller operators like Genesee & Wyoming (NYSE:GWR) and Railamerica (NYSE:RRA).

The latter two reported their May rail-traffic numbers on Monday morning. Results for Railamerica looked pretty strong -- traffic was up 10.3% on an as-reported basis and up 5.5% on a same-rail basis, which removes the impact of acquisitions. Results were fueled by strong growth in bridge traffic, as well as lumber, metals, and food shipments. On the downside, coal and auto shipments were rather weak, though neither is a great surprise.

Numbers for Genesee & Wyoming weren't quite as strong. Reported traffic in North America was up 6.5%, but down 0.1% on a same-rail basis. While the company saw higher shipments of lumber, paper, and agricultural products, lower coal shipments hurt the comparisons. Coal traffic was hurt by production problems at a mine that the company serves and a track outage in the coal-producing Powder River Basin region.

At Genesee & Wyoming's 50%-owned Australian operations, carload traffic was down 4.3% as the company continues to work through a tough year-over-year comparison to last year's record grain harvests. On the positive side, bauxite and iron shipments were pretty robust.

I've written about Genesee & Wyoming many times in the past and I still like the company quite a bit, so I won't belabor the point here again. Railamerica, though, is an interesting situation.

Larger in terms of both revenue and rail traffic, Railamerica hasn't been able to muster quite the same operational performance as Genesee & Wyoming. This railroad also has more debt. With those lower margins and larger debt, Railamerica trades at a discount to Genesee & Wyoming when you look at the forward P/E and price-to-book metrics.

Perhaps, though, things are about to turn around for Railamerica. The stock isn't well-followed, but those analysts who do follow the company seem to be expecting strong year-over-year improvements in earnings. If better operating efficiency comes as well, the stock could close some of that valuation gap with Genesee & Wyoming.

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Fool contributor Stephen Simpson has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).