Although I don't list these frequencies in my database it's not a bad idea to scan for the End of Train Device (EOT) also called a Flashing Rear End Device (FRED). These low power radios send a 'squawk' at regular intervals. An active EOT may tell you a train is nearby (typically within a mile) when no other radio traffic is heard.
Some Distributed Power Units have more power and may be heard at a greater distance than the EOTs (They have more FARS...)
452.9375 MHz head end to FRED
457.9373 MHz FRED to head end.
457.925 MHz DPU
