We have a Rand McNalley 7720. Last month in Oregon it kept trying to get me off the state HiWay I was traveling on, but it didn't say why. After the last possible place I could turn I finally found out why. There was a tunnel on the road. I pulled over and said, oops. As we sat there and wondered what to do, along came a truck that was nearly our height and it went tright though. As he went in I could tell that he had plenty of room and I knew I would be fine. We went through without issue. I don't remember the height of the tunnel being posted, otherwise I would have known it was ok. The GPS thought it was an issue. Could have been the height setting in the unit.