called out to remove a very large very old dead oak from the front yard of a very old house. The tree was not tall but very thick maybe 6 ft in diameter and one large branch maybe 50- 60 ft that was the only living thing on the entire tree streched over a road. I could not fell the tree outright even though it was only about 30 ft high. powerlines north and south and other trees to the west. The only option was drop it east east north. however the large branch was weighted to the south and other dead almost trivial branches were faced west and the entire tree was leaning south west. No biggy. I climbed and bucked the trivial branches and used a throw rope to tie off the big long branch. my plan was to cut and hindge the limb back over the yard which was not unplausible. With the limb tied off to a truck and set and a truck in the road I started cutting a 1/4 way deep through the limb. I radioed to the driver to pull a little bit, with No movement I started to cut a little deeper as in 2 inches. More then half the limb was uncut, no crackle no sway I blinked and the branch droped like a anvil landing in the road blocking traffic both ways. my help jumped out of his truck and grabed a saw as I climbed down to help clear the road. It took about a hour to clear the road and thankfully no traffic was around when it fell. We rerouted traffic as it came. As we were cutting, however we figured out why the branch fell like it did, even though the branch seemed healthy from the outside you could see how rotted the inside of the limb was. Even through I had cut less then 1/2 the branch more then half the branch was rotted. Lesson to be learned Even though a branch seems healthy or looks healthy does not mean that it is, especially when it is connected to a oak that looks like it has be dead for 20 years. I know the lesson seems dumbfounding or obvious but stuff happens and things get overlooked. anyways the rest of the drop went as planed.