The American Association of Railroads have identified a list of 96 standardized radio frequencies that are used by North American Railroads. The AAR has assigned a channel number to each of the 96 frequencies that occur in this block that is used primarily in the United States and Canada. Most railroads identify the AAR frequency channel assignments in their radios and use that designation for timetables and communications regarding use. The railroad radios employ a duplex system that can transmit on one frequency and receive on another. For example, if CSXT references a subdivision or line that is using AAR Channel 5050, the frequency that both the dispatcher and train crew would be transmitting on is 160.860 MHz. If however, the subdivision or line uses AAR Channel 1494, the frequency being transmitted on by the train crew would be 160.320 MHz and the dispatcher would be using 161.520 MHz, though on the railroad radio there would be only one radio capable of transmitting and receiving on the separate frequencies.
End-of-Train (EOT) devices (or FRED) are actually a series of communications between the locomotive and the EOT that transmit at two separate Watts and are typically limited from 3 to 5 miles. The locomotive sends its signal, a distinctive chirp, on 452.9375 MHz, while the EOT transmits on 457.9375 MHZ. Use of these non-AAR frequencies may aid in tracking down a train, as even if there is no verbal radio communication, if the train has an active (working) EOT, there will be an audible chirp.
One exception to the EOT device is that Norfolk Southern has used devices that employ their signature chirp on AAR 67, 161.115 MHz. It works similarly to the above EOT explanation, just with a lower MHz frequency rating.
The following table converts from AAR channel number to the appropriate radio frequency (MHz).