(1) The driver of any vehicle, a person operating a bicycle, and every pedestrian shall obey, and the operation of every personal delivery device shall follow, the instructions of any official traffic control device applicable thereto, and as specified in this chapter, placed in accordance with the provisions of this chapter, unless otherwise directed by a traffic or police officer, or a single flagger as provided in subsection (5) of this section, subject to the exception granted the driver of an authorized emergency vehicle in this chapter.

(2) No provision of this chapter for which official traffic control devices are required shall be enforced against an alleged violator if at the time and place of the alleged violation an official device is not in proper position and sufficiently legible or visible to be seen by an ordinarily observant person. Whenever a particular section does not state that official traffic control devices are required, such section shall be effective even though no devices are erected or in place.

(3) Whenever official traffic control devices are placed in position approximately conforming to the requirements of this chapter, such devices shall be presumed to have been so placed by the official act or direction of lawful authority, unless the contrary shall be established by competent evidence.

(4) Any official traffic control device placed pursuant to the provisions of this chapter and purporting to conform to the lawful requirements pertaining to such devices shall be presumed to comply with the requirements of this chapter, unless the contrary shall be established by competent evidence.

(5) In cities with a population of 700,000 or greater, a single flagger located at the middle of an intersection may direct traffic without a traffic or police officer present as part of a traffic control plan approved by the city.