End of Train and Head of Train Devices

Trains utilize a data telemetry system that employs a device (EOT, FRED) at the rear of the train with a flashing red marker light and a sensor for the train's air brake line. It responds to polls from the radio at the head-end by transmitting telemetry including air line pressure and speed of the train measured by GPS location technology. Almost all railroads in the U.S. use the same pair of UHF frequencies for this data. These devices put out low power, so if you hear a data burst on these channels there must be a train nearby, probably within about 2-3 miles.