What happened?
Railroad operator CSX (CSX -1.21%) has switched to a new track, and is motoring ahead -- at least, in terms of its inclusion on a key index. On Monday, the company became the newest component of the Nasdaq-100 index -- the exchange's grouping of its largest nonfinancial companies in terms of market capitalization.

CSX takes the place of KLA-Tenor, a company that makes equipment for semiconductor manufacturers. KLA-Tenor is being acquired by Lam Research in a deal worth nearly $11 billion that was agreed to last October.

Late last year, CSX transferred its stock listing to the Nasdaq, from its former home on the New York Stock Exchange.

The Nasdaq-100 is comprised of a variety of well-capitalized stocks from the exchange. Many are very prominent, such as Apple, Costco Wholesale, and Kraft Heinz.

Does it matter?
Inclusion on a well-known index is a boon for any stock. After all, a great many exchange-traded funds are mandated to build their portfolios strictly from these issuers. Also, other types of funds regularly trawl the indexes for goodies. The resulting increased demand will be a positive factor supporting CSX's share price.

It could use the help. The stock has lost more than 30% of its value over the past year, significantly underperforming major indexes such as the Dow, the S&P 500, and -- yes -- the Nasdaq-100.

So inclusion on the latter is a good thing for CSX. But it'll need to improve its fundamentals in order to help its new index move north. For example, the company posted year-over-year revenue declines in three of the four quarters in its fiscal 2015.