SearchResearch Challenge (9/25/24): How literate are people wrt road signs?

I've wondered for a while... 

... to what extent people actually understand common signs and symbols they see every day.  You probably understand all of the symbols in the above image, but based on some of the stellar driving skills I see, it's pretty clear that not everyone shares that skill.  What's the difference between the first symbol in row 2 vs. the third symbol in row 2. Do you know?  

That brings up an interesting SearchResearch Challenge for the week.  How literate are we? The goal of a roadside symbol is to be rapidly understood--you see it / you understand it.  It's supposed to be automatic.  But... 

1.  How many of the most common roadside symbols DO people understand?   

Don't just give me your estimate but find where this has actually been studied, and what the results are.  Are you surprised by what you found?  Do you think the study (studies) are valid and sound?  

Does this make you feel better or worse about your fellow drivers? 

As always, tell us HOW you found your results. 

And... 

Keep Searching! 

The basis of reading literacy is glyph recognition. Just sayin'...