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

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.

The Surface Transportation Board said on Wednesday that Union Pacific and Norfolk Southern have formally filed a notice of intent to combine, triggering the U.S. regulatory review process for a proposed $85 billion merger between the two major railroads.