Warren Buffett is working on the railroad – again.

Last month, the iconic investing guru once again displayed his enthusiasm for railroad stocks by adding to his already sizeable stake in Burlington Northern Sante Fe Corp. (BNI). After picking up 7.85 million shares of Burlington in early October, Buffett’s Berkshire Hathaway Inc. (BRK.A, BRK.B) last week added another 825,000 shares to its holdings at a price of $79.65 apiece

Buffett has been bullish on railroad stocks for the past year. Buffett made his first move on Burlington Northern in April 2007, acquiring nearly 40 million shares – close to 11% of the railroad. That August, Berkshire went shopping again, loading on an additional 3.3 million shares of Burlington. He added another 6,000 in September.

Buffett continued the trend in 2008, adding 10,300 shares of Burlington to his holdings over a two-week period that ended Jan. 22.

With the purchases made last month, Berkshire’s total stake in the Fort Worth, Texas-based railway has climbed to 18.9%.

And Burlington Northern hasn’t disappointed. Just last month, the second-largest U.S. railroad reported a 31% increase in third-quarter profit. For the three months ended Sept. 30, the company reported net income of $695 million, or $2.00 a share – a 31% increase from the year-ago results of $530 million, or $1.48 a share last year. Revenue jumped 20%, reaching $4.91 billion.

“While we are all concerned about the current financial and economic situation, we continue to be optimistic about the future of our diverse franchise and we remain confident about our long-term prospects,” Matthew K. Rose, the company’s chairman, president and chief executive officer, said in a statement.

Warren Buffett is confident, as well, though not to long ago, Buffett himself wrote off the entire railroad industry as a poor investment.