Obedience to traffic-control devices; official signs to be in proper position, etc; penalty

(a) The driver of any vehicle and the operator of any streetcar shall obey the instructions of any official traffic-control device applicable thereto placed in accordance with the provisions of this chapter, unless otherwise directed by a traffic or police officer, subject to the exceptions granted the driver of an authorized emergency vehicle in this chapter. (b) Any person violating the provisions of this section is guilty of a misdemeanor and, upon conviction thereof, shall be fined not more than $100; upon a second conviction within one year thereafter, shall be fined not more than $200; and upon a third or subsequent conviction, shall be fined not more than $500. (c) No provision of this chapter 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.