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.

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

CSX Corp. stock is up on reports that Union Pacific is interested in buying the Jacksonville-headquartered railroad company. CSX Corp.’s stock rose to its highest level of the year July 17 after a report that Union Pacific Corp. is seeking to buy one of the two major eastern railroads, CSX or Norfolk Southern Corp.