Advisory speeds are determined primarily by physical and design characteristics of the roadway. The setting of regulatory speeds, while also affected by physical and design factors, is determined in large part by existing free flow traffic speeds.

A Transportation Commission minute order, city ordinance, or county ordinance is not required for advisory speed zones but is required for regulatory speed zones. Therefore, advisory speed zones are more flexible in that they can be changed without revising existing Commission minute orders or city or county ordinances.

From the standpoint of enforcement, when a regulatory speed zone has been established and signs are posted, the speed values shown on the signs are the maximum lawful

prima facie

speeds. An advisory speed sign serves to advise drivers of safe speeds that are recommended for certain roadway conditions, such as horizontal curves. It does aid the enforcement officer, however, in determining reasonable and prudent speeds. A driver might be cited for exceeding the posted value of an advisory speed zone on the grounds that they were driving at a speed that was not reasonable and prudent for the conditions existing at the time and location.