Red is used exclusively for regulatory road signs prohibiting doing something. So, a stop sign is red because you are ...
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How to navigate highway signs without a GPS

Even without GPS you can stay oriented and drive confidently on unfamiliar highways and byways to get where you're going.
KNOX COUNTY, Tenn. — Traffic signs help guide drivers safely through intersections, neighborhoods and construction zones. But few people stop to consider where those signs come from — or who’s behind ...