Rail fans that are also amateur radio operators often use these frequencies to discuss railfanning.  Here are the "rail" amateur frequencies (simplex operation):

146.490 Mhz

146.565 Mhz

223.620 Mhz

446.050 Mhz

1294.426 Mhz

Use 100 Hz Private Line or 152 DCS.  Use varies from area to area.

In Lapeer, railfans use 145.740 Mhz with a PL tone of 67.