(a) The driver of any vehicle shall obey the instructions of any official traffic-control device applicable thereto placed in accordance with the provisions of this act, unless otherwise directed by a traffic or police officer, subject to the exceptions granted the driver of an authorized emergency vehicle in this act.
(b) No provision of this act for which signs are required shall be enforced against an alleged violator if at the time and place of the alleged violation an official sign is not in proper position and sufficiently legible to be seen by an ordinarily observant person. Whenever a particular section does not state that signs are required, such section shall be effective even though no signs are erected or in place.
Laws 1961, p. 373, § 11-201.