Good point about the rails not moving much through the magnetic field. I was actually planning on approaching the company who owns the spur line near our house and asking permission. My mentor in audio was a man named Jerry Frederick who in the late 1950's made several recordings for Audio Fidelity Records, an early adopter of the then new stereo format. He got access to a rail yard in Reading PA and hauled his Ampex 351 and a couple Neuman U47's out there and spent the day recording the vanishing steam locomotives.
I don't expect as warm a welcome as Jerry received, but I am a professional audio engineer, so who knows. I guess it's all in how I approach them.? Although I prefer the former, I could do it stealthily as well on this spur that sees one or two trains a day. The biggest problem would be hiding the mic cables, and myself in the woods, and.........waiting...
Mark Day