When an engineering and traffic investigation shows that the statutory speed limits are no longer applicable for the existing conditions, the

prima facie

maximum speed limits should be altered accordingly with a speed zone.

The types of speed zones are as follows:

Each type of zone and its use is discussed later in this chapter.

Advisory speeds may be posted within speed zones to advise drivers of a safe operating speed to negotiate roadway features. This section discusses regulatory speeds and advisory speeds and explains their differences.