Speed limit signs are essential traffic control signs, and can vary in the limit depending on the specific state that you are driving though.
Often while driving through residential streets, speed limit signs may not be seen. This is because the speed limit for most residential areas is 25 miles per hour, and this law is understood by drivers who pass their driving exams.
Many highways have speed limits set at 55 miles per hour, but this can be changed by the state and will vary. Other common limits on highways are 45 miles per hour and 65 miles per hour.