Highway Signs

So simple, yet so helpful, how would we get around with highway signage?  Yet they’re mysterious, too.  How do they stay clean and bright?  How much science went into the selection of just the right color, size, and font to make them so readable without being distracting?  Who decides which towns to highlight for north/south or east/west when you’re entering a large highway?  There’s a lot of thought behind those “simple,” old-fashioned signs, and I appreciate it.