I am a very cautious driver and during this particular 4 hr – out-of-state- round trip;I had made it a point to observe all speed signs up to apparently this small town and the speed DROPPED to "25"mph. I pulled over immediately which was only a short distance from new posted sign which was to increase your speed to 45mph. As I am from out of town, being an unknown area, it was late and I was very tired; and son had asked me a question and it must have been at this point I failed to see the limit had decreased to such an extent. (The other small towns that I had driven thru that evening seemed to be not less then 35 or 30.) "25"mph seems to be unreasonably low unless during active school session.