Which major US railroad was commonly called the L&N?

The Louisville and Nashville Railroad (reporting mark LN), commonly called the L&N, was a Class I railroad that operated freight and passenger services in the southeast United States.

Chartered by the Commonwealth of Kentucky in 1850, the road grew into one of the great success stories of American business. Operating under one name continuously for 132 years, it survived civil war and economic depression and several waves of social and technological change. Under Milton H. Smith, president of the company for thirty years, the L&N grew from a road with less than three hundred miles (480 km) of track to a 6,000-mile (9,700 km) system serving thirteen states. As one of the premier Southern railroads, the L&N extended its reach far beyond its namesake cities, stretching to St. Louis, Memphis, Atlanta, and New Orleans. The railroad was economically strong throughout its lifetime, operating both freight and passenger trains in a manner that earned it the nickname, "The Old Reliable."

Growth of the railroad continued until its purchase and the tumultuous rail consolidations of the 1980s which led to continual successors. By the end of 1970, L&N operated 6,063 miles (9,757 km) of road on 10,051 miles (16,176 km) of track, not including the Carrollton Railroad.