The "Big 5" refers to the major Class I railroads that dominate the North American rail network: BNSF Railway, Union Pacific (UP), CSX Transportation, Norfolk Southern (NS), and Canadian National (CN). Following the 2023 merger of Canadian Pacific and Kansas City Southern into CPKC, the landscape shifted, but these five remain the primary titans of the industry. In the UK, the term is less common in 2026 due to the ongoing transition into Great British Railways (GBR), which is moving private operators like South Western Railway and West Midlands Trains back into public ownership. Historically, the UK had its own "Big Four" (GWR, LMS, LNER, and SR) prior to 1948. Today, in the global context, the North American "Big 5" are essential for the movement of freight across the continent, managing over 140,000 miles of track and serving as the backbone of the supply chain for everything from grain and coal to intermodal shipping containers.