Union Pacific Corp. agreed to acquire Norfolk Southern Corp. in a $72 billion cash-and-stock transaction, forming the only US transcontinental railroad in what stands to be the industry’s largest deal ever.

Union Pacific is seeking to buy Norfolk Southern in a $85 billion deal that would create the first transcontinental railroad in the U.S, and potentially trigger a final wave of rail mergers across the country.

Union Pacific and Norfolk Southern said on Tuesday that they have agreed to a merger to create a $200 billion rail giant based on their current market capitalizations.