Most railroads use one of the AAR's specified channels.
1-6 are Canada only
7-97 are the main channels.
107-197 are "splinter" channels, which are a side effect of when the analog frequencies went to narrow band. These are rarely used
Conventionally, 1-97 are analog FMN, but AAR does permit digital communications on these channels using NXDN48 (Icom IDAS/Kenwood Nextedge). Digital channels are numbered 300+their analog channel number (so digital communications on channel 54 would be 354)
These frequencies contain no useful communications, but their presence in your vicinity will indicate the presence of a train
452.9375 - End of Train Device Telemetry (FRED)
457.9375 - Head of Train Device Telemetry (MARY)
452.9250 - DPU Ch 1
452.9500 - DPU Ch 2
457.9250 - DPU Ch 3
457.9500 - DPU Ch 4
Transit Agencies are not required to use AAR channels. While some systems use AAR channels, Many use UHF frequencies or Trunked systems