In Austin here, behind our house there are trees growing up and ivy growing onto the lines. We called every week last spring, the City had no interest in trimming it. We finally got all the neighbors to call in on dedicated days so they were getting a call almost every day.
Still, they haven't trimmed them. With the ice last week, I'm shocked the lines didn't come down.
In New York, utilities trim branches a few feet from lines periodically.
They do this because they have service quality standards set by the public service commission, and it’s cheaper to trim and maintain rights of way than to be fined or denied rate increases for electricity delivery. (Electric supply is based on variable market rates)
I'm in western Washington and there are so many trees that it is hard to not have power lines go through them. Here's my power line and my Comcast cable [1]. They are do deeply in that tree that it is in essence an extra pole for them.
Just watching the power lines while driving around, I see zillions of places like that here.
From what I read, if the power company expects the line to end up in trees (or purposefully routes a new line through an existing tree) they use a line with a special insulation designed to handle the abrasion from rubbing against the tree.
Lines that are not meant to go through trees do not have that special insulation, and if they end up going through a tree it can abrade the insulation which can be quite dangerous.
Still, they haven't trimmed them. With the ice last week, I'm shocked the lines didn't come down.