(a) The driver of any vehicle shall obey the instructions of any official traffic-control device applicable to him or her placed in accordance with this chapter unless otherwise directed by an enforcement officer, subject to the exceptions granted in this chapter.

(b) No provision of this chapter for which signs are required may be enforced if at the time and place of the alleged violation an official sign is not in approximately proper position and sufficiently legible to be seen by an ordinarily observant person. Whenever a particular section does not state that signs are required, the section is effective even though no signs are erected or in place.

(c) Whenever official traffic-control devices are placed in positions approximately conforming to this chapter the devices are presumed to have been placed by the official act or direction of lawful authority, unless the contrary is established by competent evidence.

(d) An official traffic-control device placed pursuant to this chapter and purporting to conform to the lawful requirements pertaining to the device is presumed to comply with this chapter, unless the contrary is established by competent evidence. (Added 1971, No. 258 (Adj. Sess.), § 3, eff. March 1, 1973.)