^^Kinda what I was saying. If the structural vibrations shake the nest or something flies out of a train and provokes them, it could end up getting ugly. Misting a screened-in area would make it impossible for a papery nest to hold up, so they'd end up having to nest on the part of the frame outside. The screen would keep anything from flying out from the airtime hill and spooking them as well as provide a deterrent and obstacle from any swarming insects wanting to attack.
That's my theory on why this might work but I'm not a pest control expert. Can't think of what else it might do though.