I'm impressed by the level of details in the tables of these Wikipedia articles. Exactly the kind of answer I expected, that's interesting history!

@Vince thanks. Generally, when you compare European rules and American rules - you'll notice a pattern: Europeans are gearing towards sharing and removing barriers, while Americans are geared towards simplifying things for those writing the rules. So for a continent full of people who all speak different languages with different alphabets - pictograms are a no-brainer. For a continent full of rich people trying to keep the poor people out of their way - requiring (and not providing) education is a no brainer.

The first international cooperation, including 4 road signs ; nationality plates (still used today) ; international drivers licence etc., started with the International Convention With respect to the Circulation of Motor Vehicles, signed at Paris, the 11th October 1909.

I think this is a really interesting answer, but I don't think it really answers the question. For example, the Vienna protocol mostly just adopted existing standards. It was already the case that Britain, France, Belgium, etc. were using pictographic signs before the protocol was signed. Why did Europe start adopting pictographs as early as 1909 but the US not?

@JackAidley likely to keep uneducated (= poor or minority) people from being road-legal drivers due to them being less likely to be able to read

@Hobbamok I'm not sure that explanation works. At the time these decisions were being made wasn't car ownership itself enough of a bar?

Worth noting: Europe is very diverse wrt. languages. If you want to have any chance that a driver from spain can drive in france, germany, poland etc., you cannot rely on language alone and need pictograms that are common and understood by everyone.

@Polygnome: It's true now that whether a driver in Spain can understand signs in Germany is an important consideration but I very much doubt it was a consideration in 1909 when these signs were chosen. It's also not true in Britain which switched from text a couple of decades later. The real advantage of pictograms is nothing to do with cross-language understandability: it's rapidity of understanding, especially in bad conditions.

Someone made an educational youtube video to answer exactly this question. Might be worth a watch for the interested "Why US Signs Look Different Than The Rest Of The World’s" youtube.com/watch?v=Wzr0GYfRsKI

@JackAidley wasn't car ownership itself enough of a bar - of course not, there were minorities who had money.

@littleadv: "simplifying things for those writing the rules" yes, but they complicate things for those reading the rules!

@Polygnome: and yet Spain and other countries put the English word "STOP" on red octagonal signs at intersections!

Source required for asserting that it's "mostly exclusionary/discriminatory" to expect that people who drive in the US be able to read the dominant language of the US? And not just any source, but a rational source.

@RonJohn that is akin to reading proficiency tests as a condition for voting. There's no actual need for such an expectation, it's artificially created (as the question itself suggest - you can drive perfectly fine in Germany with Russian driving license without any German proficiency or even knowing the alphabet, so why wouldn't it work in the US?)

@WGroleau yes, but they complicate things for those reading the rules! - that's the point.

@WGroleau Actually, "stop" originates from Greek and is a shared word among most European languages. It is not an "English word" as you said. merriam-webster.com/dictionary/stop#word-history

It's perfectly reasonable to use symbols when you can drive for a couple of hours either direction and be in a completely different country. Not so much when you can drive 3000 miles and "your" language is still the dominant language.

@RonJohn why not? Your reasoning is exactly the "American conservatism" I'm talking about. Do you think Europeans are more intelligent than Americans and can comprehend pictograms better? Americans are that stupid in your view that you have to literally spell it out to them? No, that's not true. That's just entrenchment in the current state and refusal to acknowledge that there may be a different solution to the same problem.

As far as reading proficiency as a condition for voting... I'm all for it. (Southern whites cheated by not grading the tests equally.) Heck, I'm all for for a history and current events test (the only problem being that nobody will agree on what should be in it).

@RonJohn good for you. But as you yourself acknowledged these tests are created in order to disenfranchise and cheat. There's absolutely no reason to not allow people who can't read to vote - they're still citizens and have the right to voice their opinions. Similarly, people who can't read should still be able to move around, and in the US it means driving because public transportation is non-existent almost anywhere.

"refusal to acknowledge that there may be a different solution to the same problem". There's no problem to solve when "everyone" can read the same continent-spanning language.

People who do not have sufficient education should not vote, and I stand by that 100%. If "your" political sees a group of illiterate people and you want them to vote for you, then (1) ask yourself why they didn't learn to read in the public schools you support so vigorously, and (2) teach them to read. They'll be grateful and inclined to vote for your party.

@RonJohn can they though? You're making an assumption that is incorrect, based in facts. Currently there's about 4% of US adults who are functionally illiterate. When these rules where created, a hundred years ago, the numbers were much much higher, and specifically higher in the populations that were targeted (minorities/poor).

@RonJohn I don't decide who people should vote for and neither should you. EVERYONE should be able to vote, even if they vote against what I believe in. Equal rights doesn't have an asterisk to it.

"Can they, though?" Ambiguous question: what specifically are you referring to?

@RonJohn There's no problem to solve when "everyone" can read the same continent-spanning language. You're commenting to fast for me :-D

"EVERYONE should be able to vote". That's why everyone has an equal right to 12 grades of education, and are expected to be able to read by age 10.

@RonJohn That's why everyone has an equal right to 12 grades of education - (a) no, everyone doesn't have an equal right to 12 grades of education, (b) the education everyone is getting is very unequal and depends on the ability of local population to fund it. So unless you support fully funded public education with the same curriculum across the whole country, that's not a claim you can even remotely start making. But that's irrelevant to this question entirely.

@user2705196 That's a great video. If that was written up as an answer to the question, it'd be bang on.

"Stop" may be a word in some languages, but that doesn't make it "not an English word." It definitely is not a Spanish or Basque word except to the extent they put it on their stop signs. Mexico uses the Spanish word "alto." I don't recall even seeing any stop signs in Honduras, El Salvador, or Perú. (But it's been a while.

no, everyone doesn't have an equal right to 12 grades of education. Who in the US doesn't have that right? Honestly, I'm curious. the education everyone is getting is very unequal and depends on the ability of local population to fund it. States and the Feds give poor districts block grants. unless you support fully funded public education with the same curriculum across the whole country. The dreaded No Child Left Behind had national standardized testing, which meant everyone had to learn the same things to pass the tests.

@user46971 these two claims are completely orthogonal. You can both design something to be exclusionary and refuse to change it because of the sunk cost. One decision came half a century before the other, and both saying that the original decision was driven by the generally common-pattern exclusionary policies of the time and that the decision not to change the overall system 50 years later because the hurdles had been overcome in other ways and the benefits are small can be true.

@RonJohn "No Child Left Behind" was a part of the law passed in 2001, we're discussing a decision made a hundred years beforehand.

I think quite a few people here are confusing my argument that the decision was motivated by the exclusionary intentions as an argument for preserving the current state now. That's not what I said, repeatedly. If anyone wants to argue that 100 years ago everyone had equal right to education and there was absolutely no expectation of disparity in literacy rates between different slices of population in the US - good luck with that argument.

The explanation to preserving the current state now is the general conservatism of the American populace, which has been demonstrated quite clearly in this very thread. It's not necessarily a bad thing, sometimes being conservative is good (although Americans tend to equate "conservatism" to "my way or high way" in the current American political discourse).