Which railroad does Warren Buffett Own?

I'm curious to know, which specific railroad does Warren Buffett, the renowned investor and businessman, currently own? Given his reputation for shrewd investments and his substantial portfolio, I'm eager to learn about the railway company that has captured his attention and investment dollars. Is it a well-established name in the industry, or perhaps a lesser-known but promising venture? I'm intrigued to discover the details behind this particular investment of his.