I use to go to a local campground a lot. I had to drive under an oak limb to get into the campground and never had a problem, until ... One summer day it rained and the added weight was just enough to make the limb sag enough to collect my AC unit. It cost around $2000 to repair the roof. I'm much more careful now. If there's any doubt that I'll make it, I won't even try. It's nice to carry something to measure with. I've been to campgrounds that had run their own overhead lines and they were only about 11 feet off the ground. I had a long tape measure with me and was able to determine that they were a little too low to go under.