Class I railroad in the context of "BNSF Railway"

The Pennsylvania Railroad (reporting mark PRR), legal name as the Pennsylvania Railroad Company, also known as the "Pennsy," was an American Class I railroad that was established in 1846 and headquartered in Philadelphia, Pennsylvania. At its peak in 1882, the Pennsylvania Railroad was the largest railroad (by traffic and revenue), the largest transportation enterprise, and the largest corporation in the world.

Over its existence, Pennsylvania Railroad acquired, merged with, or owned part of at least 800 other rail lines and companies. At the end of 1926, it operated 11,640.66 miles (18,733.83 kilometers) of rail line; in the 1920s, it carried nearly three times the traffic as other railroads of comparable length, such as the Union Pacific and Atchison, Topeka & Santa Fe railroads. Its only formidable rival was the New York Central Railroad (NYC), which carried around three-quarters of the Pennsy's ton-miles.

The Canadian National Railway Company (French: Compagnie des chemins de fer nationaux du Canada) (reporting mark CN) is a Canadian Class I freight railway headquartered in Montreal, Quebec, which serves Canada and the Midwestern and Southern United States. It is one of Canada's two main freight rail companies, along with Canadian Pacific Kansas City.

CN is Canada's largest railway, in terms of both revenue and the physical size of its rail network, spanning Canada from the Atlantic coast in Nova Scotia to the Pacific coast in British Columbia across approximately 20,000 route miles (32,000 km) of track. In the late 20th century, CN gained extensive capacity in the United States by taking over such railroads as the Illinois Central.

The Kansas City Southern Railway Company (reporting mark KCS) is an American Class I railroad. Founded in 1887, it operated in 10 Midwestern and Southeastern U.S. states: Illinois, Missouri, Kansas, Oklahoma, Arkansas, Tennessee, Alabama, Mississippi, Louisiana and Texas. KCS owned the shortest north-south rail route between Kansas City, Missouri, and several key ports along the Gulf of Mexico.

The focus of the routes was the fastest way to connect Kansas City to seaports, since it was only 800 miles from Kansas City to the Gulf of Mexico compared to 1,400 miles between Kansas City and the Atlantic Ocean ports.

The Norfolk and Western Railway (reporting mark NW), commonly called the N&W, was a US class I railroad, formed by more than 200 railroad mergers between 1838 and 1982. It was headquartered in Roanoke, Virginia, for most of its existence. Its motto was "Precision Transportation"; it had a variety of nicknames, including "King Coal" and "British Railway of America". In 1986, N&W merged with Southern Railway to form today's Norfolk Southern Railway.

The N&W was famous for manufacturing its own steam locomotives, which were built at the Roanoke Shops, as well as its own hopper cars. After 1960, N&W was the last major Class I railroad using steam locomotives; the last remaining Y class 2-8-8-2s would eventually be retired in 1961.

Conrail (reporting mark CR), formally the Consolidated Rail Corporation, was the primary Class I railroad in the Northeastern United States between 1976 and 1999. The trade name Conrail is a portmanteau based on the company's legal name. It continues to do business as an asset management and network services provider in three Shared Assets Areas that were excluded from the division of its operations during its acquisition by CSX Corporation and the Norfolk Southern Railway.

The federal government created Conrail to take over the potentially profitable lines of multiple bankrupt carriers, including the Penn Central Transportation Company and Erie Lackawanna Railway. After railroad regulations were lifted by the 4R Act and the Staggers Act, Conrail began to turn a profit in the 1980s and was privatized in 1987. The two remaining Class I railroads in the East, CSX Transportation and the Norfolk Southern Railway (NS), agreed in 1997 to acquire the system and split it into two roughly-equal parts (alongside three residual shared-assets areas), returning rail freight competition to the Northeast by essentially undoing the 1968 merger of the Pennsylvania Railroad and New York Central Railroad that created Penn Central. Following approval by the Surface Transportation Board, CSX and NS took control in August 1998, and on June 1, 1999, began operating their respective portions of Conrail.

The Atlantic Coast Line Railroad (reporting mark ACL) was a United States Class I railroad formed in 1900, though predecessor railroads had used the ACL brand since 1871. In 1967, it merged with long-time rival Seaboard Air Line Railroad to form the Seaboard Coast Line Railroad. Much of the original ACL network has been part of CSX Transportation since 1986.

The Atlantic Coast Line served the Southeast, with a concentration of lines in Florida. Numerous named passenger trains were operated by the railroad for Florida-bound tourists, with the Atlantic Coast Line contributing significantly to Florida's economic development in the first half of the 20th century.

Canadian Pacific Kansas City Limited, doing business as CPKC (known as Canadian Pacific Railway Limited until 2023), is a Canadian Class I freight railway, headquartered in Calgary. It operates about 32,000 kilometres (20,000 mi) of rail in Canada, Mexico, and the United States, and is the only single-line rail corporation ever to connect the three countries.