A siding long enough to hold an entire train, allowing a meet or pass between two trains on a single-track mainline. The length and spacing of passing sidings are key determinants of mainline capacity. Extending or adding passing sidings is a common capacity improvement investment.
A track parallel to and connected at both ends to the mainline, used for storing cars, allowing trains to pass each other, or serving customers. Passing sidings are a fundamental capacity tool on single-track mainlines. Customer sidings are used for loading and unloading.
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.
A wayside device that conveys authority and speed information to train crews by displaying light aspects or physical positions. Signals are the fundamental mechanism for maintaining safe train separation in a signaled territory. Signal aspects are governed by rulebooks that define what each combination of lights means.
A safety system mandated by Congress after the 2008 Chatsworth collision that automatically enforces speed limits, prevents train-to-train collisions, and enforces temporary speed restrictions, overriding human error. PTC uses GPS, wireless communications, and digital track maps to monitor and control train movements in real time. All Class I railroads completed PTC implementation by the 2020 deadline.