I use the rail planner with the control key, so it loops around all over the place avoiding trees. It's really hard to select these rails afterwards without including other rails in with the mix. I'm wondering if there's a better way for this thing to work than selecting an area.

I think, what would really like, is to select an anchor signal and a direction, and the planner would then place signals all along the track in the indicated direction until it encountered a place where the track forked or until it encountered another signal. That might be really hard to do though.

I don't think it's that hard. It already does most of that already. It picks a piece of rail, and continues on this rail until it reach a track outside the selection area or one already visited. I'd just have to update the stop condition from "until outside the selection area" to "until end of segment".

I think that can be the shift behaviour, rather than what I currently have as the shift behaviour.

I'll have a look at this weekend, no promises yet though