The weight of rail measured in pounds per yard, which determines its load-carrying capacity, stiffness, and durability. Mainline tracks typically use 132 to 141 lb/yd rail while branch lines may use lighter 90 to 115 lb/yd sections. Heavier rail supports higher axle loads and train speeds.
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 transverse member placed beneath and perpendicular to the rails to maintain track gauge and transfer load to the ballast and subgrade. Traditional ties are wood (often treated with creosote), while modern alternatives include concrete, composite, and steel. Tie replacement is one of the largest track maintenance cost items.
The granular material, typically crushed stone or gravel, placed under and around ties to provide a stable, well-drained foundation for the track structure. Ballast distributes axle loads to the subgrade, provides drainage, and resists lateral and longitudinal movement of the track. Ballast maintenance and tamping are routine track maintenance activities.
The primary high-capacity route of a railroad, characterized by heavy traffic, higher track speeds, and the most sophisticated signaling and infrastructure. Mainlines carry the bulk of a railroad's revenue ton-miles and receive priority in capital investment. They connect major terminals and industrial centers.