We were traveling in the dark. The route number told us to make a turn north as we merged with another major highway. Then we relaxed and in a very short time missed the sign that told us to turn east again. In the dark and not watching carefully on an unfamiliar road, we missed the sign. Sometime later we realized that we were not seeing signs for our route and the exit signs pointed toward unfamiliar towns. We realized that we had not read the signs carefully enough. It cost us an hour of travel and added about fifty miles to our trip.