Koppers is a stock Cramer first recommended a little over a year ago, and it is up about 46% since then. It is "an oblique play" on railroads, he said. It makes rail ties and rail splitters. The "trick" with Koppers is that it's really a chemical company, Cramer said. Rails account for just 37% of the company. However, when you get a cycle, "impure" plays such as Koppers are great "because The Street doesn't notice them until they report great numbers," he said. Cramer called Koppers "a subtle way" to play the railroad boom and suggested that people get aboard the stock.

Cramer told the caller he had recommended GBX off of Stockpickr.com, in the hopes that he could "bust some shorts." However, then he saw the error of his way. Cramer said that Greenbrier is in fact a rail car play, but it is not the one he wants people to own.

Another way to play the rail cycle, he said, is with Trinity Industries (TRN), the largest manufacturer of rail cars in the U.S. Trinity is a "pure play" and the "one to own," Cramer said. It is kind of a confusing stock that tends to turn people off, but if people take a closer look at it they'll see Trinity is "all about the rails," he said. Because ethanol needs to be transported by rails, Trinity, which makes ethanol rail cars, will benefit, he said.