Positive Train Control (PTC)
Positive Train Control (PTC) is a North American mainline safety overlay, mandated by US law, that automatically enforces speed limits and movement authorities to prevent train-to-train collisions, overspeed derailments, work-zone incursions and movement through misaligned switches. It combines GPS, 220 MHz radio and wayside interface units.
How it works
An onboard computer tracks the train's position via GPS and a track database, receives movement authorities from the back office, and polls wayside interface units (WIUs) for the status of signals and switches ahead. If the crew does not respond to a warning, the onboard system applies the brakes.
Most US Class I railroads run I-ETMS (Interoperable Electronic Train Management System) so that locomotives can operate across each other's territory. Communication typically uses a dedicated 220 MHz radio network with cellular and Wi-Fi as supplementary paths.
Why it matters for security
PTC links locomotives, wayside equipment and back-office servers into one interoperable network spanning multiple railroads. Loss of radio coverage or corrupted status messages can force trains to slow or stop, and the back office is a shared, high-value system. Monitoring PTC traffic for anomalies is a recurring requirement in US rail cybersecurity directives.
Related solution
PTC system protection for freight rail
Securing onboard, wayside and back-office PTC systems across long-distance freight networks.
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