Landmark mergers in the past - such as the creation of BNSF and between Union Pacific and Southern Pacific - have set the stage for today's concentrated rail network, often triggering both operational gains and regulatory pushback. Here are some of the largest railroad deals in the past three decades:

Charleston’s claim to railroad fame comes into focus as Norfolk Southern Corp. considers a merger with Union Pacific that would form a transcontinental giant

Speculation follows reports of Union Pacific's pursuit to acquire Norfolk Southern, suggesting wider industry consolidation.

Union Pacific said on Tuesday it would buy smaller rival Norfolk Southern in an $85-billion deal to create the country's first coast-to-coast freight rail operator.

On Tuesday, Union Pacific, which operates mostly in the Western U.S., announced that it would acquire Norfolk Southern, which operates in the East, for $85 billion. The deal would create the largest freight rail network in the country,