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The other day I was driving behind a bus and it had a sign on the back that read "This vehicle does not turn on red" and the word "red" was colored red while the other text was black. Is there an actual purpose to this?

At first I thought that maybe it's to aid someone that is unfamiliar with what color the word "red" represents, but then I started thinking about what the sign is actually for. I would assume that the target audience for that sign is other drivers; presumably so that they would exercise extra caution. How likely is it that someone that is licensed to drive would be able comprehend that sentence and understand the implications of it, but then not know what color "red" is?

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What the hell does it mean that it "does not turn on red"?!? Does that mean that it doesn't have working rear lights? If yes: how can someone allow that kind of vehicle!?! –  Bakuriu May 11 at 18:24
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@Bakuriu In the USA cars are allowed to turn right on a red traffic light if the road is clear. But per the question I understand heavy vehicles like buses would not because they are too bulky. Source: I am from the UK but have visited the USA. –  steveverrill May 11 at 20:07
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@Bakuriu USA native here, steveverrill is correct. It is allowed (in the absence of a sign stating otherwise) to turn right when you're stopped at a red traffic light and the lane you're turning into is clear. It's not required to do so, but so many people do it that many drivers have come to expect it (and some will even honk impatiently if you don't). Buses and trucks often have this text on the back so the drivers behind them know not to expect the bus/truck to turn when stopped at a red light. –  David Z May 11 at 21:54
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Just to convince the rest of the world that we're even madder than they knew: turning right on red is allowed by default in every one of the United States except Indiana. And there are other minor traffic rules that vary from state to state: what the speed limit is in school zones, whether rain requires you to turn on your head lights, and things like that. –  dmckee May 11 at 23:43
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@Bakuriu or just don't turn on a red light. No matter how much people may honk at you, you don't have to do it. –  David Z May 12 at 13:52

2 Answers 2

up vote 22 down vote accepted

You are talking about Stroop Effect.

stroop effect by Wikipedia

It is more intuitive and easier to remember to show a colour name in the colour itself.

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However,this also has the opposite effect when users unintentionally associate a word with a colour without necessarily realizing it. This is particularly a problem with colours like green or red that are used for more than one purpose or context. –  Michael Lai May 11 at 22:43

Probably not applicable in the traffic light context but you might also consider colour-blind people. Some will not be able to tell you if something is red but they typically can detect shades. So, for example, you might have "Really important stuff indicated in blue." (where blue is coloured blue). A colour-blind person would be able to match the shade of the word "blue" with the "important stuff".

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