(a) No person may operate a motor vehicle on any highway in American Samoa at a rate of speed in excess of 30 miles an hour except as otherwise provided in this title.

(b) The Commissioner shall determine, upon the basis of an engineering and traffic investigation, such other maximum speeds as shall be reasonable and safe under the conditions found to exist at any intersection or any other place on the highways of American Samoa. Such maximum speeds shall be effective when appropriate signs or markings giving notice thereof are erected, and may be declared to be effective at all times or at such times as are indicated upon the signs; and differing limits may be established for different times of day, different types of vehicles, varying weather conditions, and other factors bearing on safe speeds, which shall be effective when notice thereof is given by official traffic-control devices.