The rail gauge of 4 feet 8.5 inches (1,435 mm), used by approximately 55% of the world's railways including all Class I railroads in North America. Standard gauge enables interoperability of equipment across the North American network without gauge conversion. It was adopted as the U.S. standard in the 1880s.
The distance between the inner faces of the two running rails of a railroad track. North American and most world railroads use standard gauge of 4 feet 8.5 inches (1,435 mm). Gauge determines equipment compatibility and is a fundamental physical standard of the railroad network.
The transfer of freight cars and the accompanying waybills between two connecting railroads at a junction point. Interchange rules, governed by AAR circulars, define responsibilities for car condition, billing, and liability. It is the mechanism that enables single-bill, multi-railroad shipments across the North American network.
The principal trade and standard-setting organization for the major freight and passenger railroads in North America. The AAR develops and publishes interchange rules, equipment standards, safety standards, and technical specifications that govern how railroads interact with each other. Membership includes Class I railroads, Amtrak, and many regional and short line railroads.