Class I railroads are the largest freight railroads in the United States, defined by their operating revenue. As of 2021, they must generate at least $505 million in annual revenue to qualify for this classification. These railroads play a crucial role in the transportation of goods across long distances, connecting various regions and industries. There are seven major Class I railroads in the U.S., including Union Pacific, BNSF Railway, and CSX Transportation. They operate extensive networks of tracks and services, facilitating the movement of bulk commodities, intermodal containers, and other freight, significantly contributing to the economy.