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A 2009 regulation in the US specifies that street name signs "shall be composed of a combination of lower-case letters with initial upper-case letters" (source). For example, "DOLLYWOOD" would not be okay, but should instead be "Dollywood".

I suppose the argument is that lowercase is easier to read, while all-caps is easier to notice. Although my common sense doesn't disagree, are there any studies backing this up?

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Lowercase letters differ in size, but CAPS DO NOT. Therefore there is a greater variation, making it easier to read. Since I don't have a source at hand, to back this up, <strike> I give you advice: JUST BELIEVE ME </strike> I post this as a comment. –  user unknown Aug 23 '11 at 1:00
IMO a wall of CAPS is very annoying to read, normal wall of text is marginally better, paragraphed CAPS is still annoying, and normal paragraphed text is best –  ratchet freak Aug 23 '11 at 1:12
Many legal agreements have section headings that are written entirely in upper-case letters, which seems to make it easier to find each section (particularly when they're also in bold). Seeing an entire paragraph written in upper-case can be slightly more tiring to read though. –  Randolf Richardson Aug 23 '11 at 4:00
@Randolf Richardson: Indeed. A good example is the NO WARRANTY section of many software licenses. The purpose is to be conspicuous, but I tend to ignore paragraphs containing all-caps text. It'd be better if "NO WARRANTY" was a header, followed by mixed-case text. –  Joey Adams Aug 23 '11 at 6:29

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up vote 14 down vote accepted

Mostly yes, but it depends. For fixed-message road signs, mixed-case outperforms upper-case, according to Garvey et al. (1997), Effects of font and capitalization on legibility of guide signs. Transportation Research Record 1605:73. In their introduction, they state that

Forbes et al. (2) conducted what are perhaps the definitive studies of the difference in legibility between text depicted in all uppercase letters and that depicted in lowercase with initial capital letters. When upper- and mixed-case words occupied the same sign area, Forbes and his colleagues found a significant improvement in reading distance with the mixed-case words. It must be understood, however, that these results were obtained with a recognition task. That is, the observers knew what words they were looking for. In instances in which the text is not known to the observer, improvements with mixed-case words are not evident (1,2). Although mixed-case superiority is fairly well accepted in the traffic engineering community [Markowitz et al. (4) provided specific information suggesting the use of mixed-case lettering for conventional road guide signs in 1968], conventional road guide signs still are being created with all uppercase letters.

Assuming that the authors can summarize prior research, I didn't hunt down the Forbes reference; here's the info for those who want to look at the original source: Forbes, T. W., K. Moscowitz, and G. Morgan. A Comparison of Lower Case and Capital Letters for Highway Signs. Proc., 30th Annual Meeting of the Highway Research Board, Washington, D.C., 1950.

After testing their new font, "Clearview" (which is, to me, indeed easy to read), Garvey et al. find again that

The mixed-case Clearview characters outperformed the all-uppercase Series D by as much as 14 percent in daytime and 16 percent at night, as long as the mixed-case font subtended an equivalent sign area. If the mixed-case font took up less sign space, as with the Clearview Condensed at 100 percent, there was no difference between mixedcase and all-uppercase characters. During daytime testing there was no difference between Series E(M) and any comparably sized Clearview font (i.e., Clearview and Clearview at 112 percent). At night, however, with both high-brightness materials, the Clearview font at 112 percent outperformed the Series E(M) by 16 percent.

Note that things are different for the variable-message road signs (i.e. the ones you may see at road construction sites. There, all uppercase is better, according to Collins and Hall, (1992). Legibility and readability of light refecting matrix variable message road signs, Lighting Research and Technology 24:143.

In general, letters with any regular shaped pixel, a width/height ratio approaching 1.0, an upper case font and a letter separation of two pixels were found to be most effective.

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