Hi Chev and railfans,
To find active frequencies in your area you search for them, right? Search from 160.215 to 161.565 and log what you hear, computer control and search logging software is helpful. That gives you a starting point you can use to find what each is used for and
http://www.railroadradio.net/ is a good place to look.
Just because you live near the tracks doesn't mean a thing if the closest tower is many miles away. Fixed transmitter locations depend on the railroad and where they are determines what you hear, right? I live a block away from New Jersey Transit's Shore Line and have two yards and several towers within range and Conrail (CSX/NS Shared Assets) isn't far but the transmissions on a freight line are few and far between compared to a passenger line and the transmitters are much farther apart. NJT chatters all the time but Conrail makes a few transmissions in the middle of the night, most of the action is up north and too far to be heard.
One interesting note, you may occasionally hear transmissions on one road's channels but they're actually another that shares trackage and sometimes it's in another area altogether. For example I sometimes hear NJT on Amtrak and Conrail frequencies, thier Trenton Main runs on Amtrak's Northeast Corridor and the Port Jervis (NY) Line runs on CSX's Southern Tier. Since they switch to those frequencies when operating there nothing stops them from using them as "private" channels on thier home ground.
"I'm the train they call The Spirit of New Orleans... I'll be gone 500 miles when day is done."
Arlo Guthrie