Sometimes, you might be able to get a twofer, in that transmission lines often run very near tracks. However, somebody would be getting inferior imagery if they weren't the focus of the camera. But if the tracks are near enough to your lines with chargers installed, it might still allow some low hanging fruit after your initial client win. Maybe make your base stations cable of handling two drones; one for the power lines, the second for the tracks. I'm more rambling than tempting your focus. Just fun to think about.

Curious, does a straight flyover of lines/towers/poles offer the footage necessary, or do you have to orbit the support structure to see enough detail? That would obviously add much more time/expense.