Answer: How literate are people wrt road signs?

 We live in a world full of symbols... 

Many of which are essential for living a safe life--such as the signs you see on the roadside every day.  

But a real question is to what extent people actually understand common signs and symbols they see every day.  

I assume that you understand all of the signs above, but it's not clear that not everyone shares your skill.  

What's the difference between the first symbol in row 2 vs. the third symbol in row 2. Do you know?   (Answer: "curving road" on the left, "slippery road" on the right.)  

So the Challenge this week is not to identify these signs, but to understand the larger question:   

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

We're looking for a study of how many road signs people understand.  How do you approach such a question?  

Added later:  I should have made it clear that I was asking only about road sign understanding in the US.  As several readers pointed out in the thread over on LinkedIn, different countries have VERY different expectations about how much training one needs before even taking a driver's test.  The US seems to have a fairly low bar for passing the drivers' test!

This is a fairly open question, but I know we're looking for a study of "road sign literacy" that would measure how many people recognize (correctly!) a set of common road signs.  

My first query was: 

     [ how well do drivers understand road signs ] 

Giving this as the first result: 

That's really interesting.  But when you click through to the article, (Many Americans Struggle to Identify Road Signs) you'll quickly find that it's a summary of other work that's just published on the Automotive Fleet website.  (A website for car fleet management.) It's not bad as a summary, but I like to read the original work and get more of the context. 

In this case, that web page summarizes a report by MyVision.org on road sign readability, "Read the Road: Sign Struggles and Dangerous Distractions." Their analysis is pretty good and filled with interesting results. But again, MyVision.org is a LASIK eye surgery provider, not a specialist in reading or automobile safety.  

The main claim in this study is that 20% of respondents did NOT know what these signs mean when based on shape alone,  although they understand "merge" and "yield" correctly. For example, when looking at road signs based on their shape and color but without any text, only 73% of Americans could accurately identify a road construction sign. Obvious question: Do you know what sign this is?  

But as I read this article I find myself filled with questions:  Who did this study?  They say that"We surveyed more than 1,060 drivers"--how did they select the drivers?  Who is "we" in that sentence? How was the survey given to them?  Why did they test road sign shape without text? Questions abound!  We must go deeper.  Does this article lead anywhere useful? 

I have to tell you that I failed to figure out who/when/where the original article was published.  It sounds good and look interesting, but there's no there there.  (I even emailed the people listed as the contact point--no replies yet.)   Update: I got an answer back from the original authors who say that the MyVision.org web page is the only available version of their report; no other methodological details are available.

So we have to take those results with a grain of salt.  They might be great, but who knows? 

I shifted my search to a Scholar.Google.com search: 

     [study understanding road signs] 

And quickly found a relevant article "Comprehension and Training of International Road Signs" published in the very reputable Proc. Human Factors and Ergonomics Society (2004).  (Note: you might have to pay for access.) In this study (done in North Carolina), testing of 100 people (60 women, 40 men) on 100 international road signs discovered that understanding varies a lot!  

Examples: different signs and recognition rates--Stop sign (100%), Road works (92%), road narrows (42%), road closed (29%).  

They also tested the participants after a short training on what the signs mean. Good news: training really works, improving recognition rates to nearly 100%.  (That's not surprising, but what they SHOULD have done was to re-test participants after a couple of weeks to see if the training actually lasted for more than a day.)  

With this search query I also found a fascinating document: The Development and Evaluation of Effective Symbol Signs (1982), a truly masterful study produced by the US National Bureau of Standards to identify the issues around making effective signage that people would understand. (For both road and non-road signs.) In one study (dating from the late 1970s) people were asked to determine what  symbol they were looking at:  

“... the authors found that some symbols, such as ‘telephone,’ ‘no smoking,’ and the conventional U.S. ‘exit’ sign, were understood by almost all the subjects tested. Yet other symbols, such as ‘blind alley,’ ‘do not block,’ and ‘break glass,’ were understood by only 20-25 percent of the subjects. Not only were some symbols not understood, several symbols were given a meaning opposite to that which was intended. Thus, ‘no exit’ or ‘blind alley’ was interpreted as ‘exit’ or ‘safe area’ by almost all subjects who gave a definition for this symbol.”

Ooof.  That's consistent with other studies, but is frightening.  Not only are many road signs not understood, by everyone, but people will latch onto the OPPOSITE interpretation of a sigh.  Bad idea.  

Shift in strategy:  Even though I used the word "literacy" and "understanding" in my framing of the challenge, it became clear by reading these articles that the preferred terms are "comprehension" rather than literacy, and "traffic sign" rather than "road sign" or "symbol."  

New query: 

     [traffic sign comprehension] 

And that in turn leads to a few more studies: "Comprehension of traffic signs with symbolic versus text displays" Transportation Research Part F: Traffic Psychology and Behaviour (2013) This study in Israel shows that symbols alone (that is, without text) are understood about 51% of the time, while symbol + text is nearly 100%.

That's better than the North Carolinian results. BUT they also found that interestingly, signs that were misunderstood to mean the opposite of their true meaning (as in the previous study) were generally not less familiar than signs that were answered incorrectly or partially correctly. Thus, familiarity alone was not a guarantee of good comprehension.

I can go on--but after looking at several studies, the overall conclusion is best summarized as "people mostly recognize the common signs, but rare signs are often not understood, or worse, are thought to mean the opposite of their intended meaning!"  

You could design your own study... if you're curious, here's the master list of all US traffic signs.    

A small section of the US DOT master signage list.

SearchResearch Lessons

1. Persistence!  As usual, the quick and obvious search often gives you information that looks good, but usually requires a bit more digging to validate.  Be one of those searchers who persists.  

2. Learn the preferred terms of art as you read.  As you saw, I shifted my terms as I read the papers.  Pay attention as you search to the language you're seeing.  It can inform your later searches with much better terms.  

Keep Searching! 

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

BTW, this is the throne name cartouche of Thutmose III,  the sixth pharaoh of the Eighteenth Dynasty,.  Details here.  (Men kheper Ra, "Lasting is the Manifestation of Ra" as seen in the Abydos Canon no. 70 and  Saqqara Canon no. 8  Cf: Beckerath, “Handbuch der ägyptischen Königsnamen”, 2nd ed. MÄS 49 (1999). 136-137, 6:T1