The merger would create the United States’ first coast-to-coast rail network, spanning 50,000 miles and 43 states.

Union Pacific offers $20 billion cash and one share of its stock to buy Norfolk Southern Tuesday in a merger that could trigger the final wave of railroad mergers across the country

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.