The driver of any vehicle shall obey the instructions of any applicable official traffic control device unless otherwise directed by a traffic or police officer [subject to exceptions granted the driver of an authorized emergency vehicle.]

The traffic control devices must be in proper position and sufficiently legible to be seen by an ordinarily observant person. [However, if a state statute imposes a traffic rule, but does not state that informative traffic devices are required, the statutory rule governs even though no devices are erected or in place.]

[Official traffic control devices placed in positions approximately conforming to the requirements of law are presumed to have been so placed by official act or direction of lawful authority and are presumed to comply with the requirements of law, unless the contrary is established by competent evidence.]