Union Pacific is reportedly considering acquiring a rival railroad, sending shares of CSX and Norfolk Southern higher.

CSX has a $62.5 billion market capitalization, compared to $58.7 billion for Norfolk Southern. Union Pacific is the largest of the three S&P 500 railroad stocks, with a $138.1 billion market cap. BofA also cited CSX's internal improvements in the upgrade, according to The Fly investment site.

The rails sector is on high alert following reports that Union Pacific (UNP) is focused on acquiring Norfolk Southern (NYSE:NSC), which could create the nation's first coast-to-coast rails network if the deal cleared regulatory and White House scrutiny.