Great article that is worth the read if you are an environmental graphic designer or wayfinding enthusiast.
I was surprised by the sheer variety of type styles I discovered on my journey. Even though all road signage systems are intended to be as legible as possible, there appears to be no consensus on how to achieve this in terms of type treatment. Some road signs used grid-based typefaces, some were extremely wide geometric typefaces with the simpler forms of a and g, some very thin, and some very heavy. These days, with digital sign production, we see more and more print typefaces (like Helvetica) and even system typefaces (like Arial) on signs. The old geometric and grid-based typefaces were mostly a product of the drawing and sign-production methods of the time. Today we can choose from hundreds of very legible, high quality print typefaces; however, during my own research I remained skeptical that simply plastering our best print typefaces on road signs would be the best way to go.