Traffic signals for the colorblind

I don't know why this never occurred to me before, but today on Twitter, several people who are attending the 2011 Accessibility Summit pointed out that traffic lights aren't, traditionally, accessible. Think about it. If you're colorblind, does red, yellow, green tell you as much information as you need, as easily and quickly as you need to know it?

Turns out, some Canadian provinces deal with this by adding shapes to the lights, as well as colors. This is an example from Halifax, Nova Scotia. Thanks to Seth Meranda for linking it!

Image: Sprocket at en.wikipedia. Used via CC.


  1. Or they could have just put the red on top, green on the bottom like they do everywhere else.

    Sure this wasn’t Newfoundland?

    1. Having red on the top and green on the bottom is definitely enough information when the light has all three colors. The problem – for me, at least – is stand-alone blinking lights. Red and yellow lights look exactly the same, and I’m always asking other people in the car if these lights are red or yellow. This is usually met with no response, I suppose because people forget that I’m colorblind and the question is meant seriously. Blinking red lights are usually accompanied by stop signs, but not always. I usually just try to pay attention to what other drivers are doing, or failing that err on the side of caution and stop. But the added shapes would certainly be welcome.

    2. Traffic lights tend to be put sideways where high winds are a problem.  Colorblind or not, I don’t think you’d want want of those things to snap off and land on your car.   On the plus side, it’s not like we put them in a different order every time, when it’s sideways red is always on the left and green is always on the right.  ;)

    1. FWIW, the rest of the world (outside of North America) deals with this non-problem by having traffic lights mounted vertically, with red on top and green at the bottom :)

      Can’t we have both? I like shapes. I mean, look at that traffic signal…just look at it!

    2. Horizontal lights aren’t universal in North America, and indeed, most jurisdictions in North America use vertical traffic lights.

  2. That’s neat, but I though color blindness meant the colors appeared differently, not without distinction from one another. Much appreciation to anyone who knows for sure.

    1. There are several kinds of color blindness, but they generally involve two wavelengths of light appearing to be the same color. In red-green color blindness, the most prevalent of all color blindness, red and green appear to be the same color, hence the problem.

      1. Thanks!

        Perhaps it has something to do with the cone cells of the eye. Or perhaps its a difference in the brain’s visual processing faculty. Hmm…wishing I had more time to research :/

        1. It’s generally an issue with one of the three sets of cones being ‘miscalibrated’, as it were- most sensitive to the wrong frequency of light. At the same time, the brain still treats the signals it receives as though the sensors were correct, which is where the problem comes up.

    2. I’m red-green color deficient.  In very general terms, you’re right.  There are things I can see in certain slides of the Ishihara test (the circle made of different colored dots) that color-uh…color-normal(?) people can’t see, so that indicates that you know, that I’m making different distinctions than other people are.

      However, the essential problem is that I often can’t distinguish green from red.  And more often, when they share the same value (that is, of brightness and darkness) I can distinguish between them, I just don’t know which is which.  I’ve owned articles of clothing for years thinking that they’re green only to discover that they’re red or brown later.  And usually after that point, my eyes “correct” somehow, and I re-learn that color.  I vividly remember one day walking towards a bright green tree when it was pointed out that there were bright red flowers in said tree, and they suddenly popped into existence.  It’s usually not that weird, but it can be.

      For me, this is not the case with stop lights.  The red is a warmer, orangey-red that I have no trouble with, and the green is a pale, under-saturated green that I also have no problem with.  There are, however, people who have greater degrees of colorblindness than I do, and that includes people who have absolutely no color information in their vision whatsoever.  I hope that clears that up.

      1. I hope that clears that up.

        Quite, and thank you. Lots of great explanations here. I guess there’s more to color-blindness than meets the eye ;-)

  3. Brotherpower is right. the colourbluind don’t go by the colour of the lights, we go by the position of the lights. Red is on top, green on the bottom. If the lights are sideways due to space constraints the red is always on the left and green always on the right.

    1. There are different forms of color blindness. I am red-green color deficient. I cant distinguish red from green at a distance. Up close its obvious but when coming upon a light where I can just tell its lit but cant see which position its in the color is indistinguishable for me. Once I am closer I can see the difference.

  4. The position of the lights doesn’t work when the signal is a single flashing light and the driver has to discern whether it’s yellow or red.

      1. In the US, a flashing yellow light means slow down as you go through the intersection, and flashing red means stop and then proceed if clear. It’s common to switch to flashing lights late at night so drivers don’t have to wait for light changes on empty streets.

  5. This is done in North America.  Almost every stoplight in America is vertical for just this reason.   An interesting history on why green and red is at the Straight Dope:

    Short version, long ago at train crossings, red was stop, green was Caution, and white (clear) was go.  Not only could go be confused with any light, but in 1914, a red lens broke or fell out, leaving white, causing a crash.  Green became go.

  6. this really is a non-issue, colorblindness is why there are separate lights, and red is always on top for vertical lights and on the left for horizontal.

    being color blind means you can’t tell the difference in colors according to the type you have, the most common is red-green, so a person can’t tell if the light is red, or green, but they can see that it’s on.  we had a guy on our team that was rg colorblind, and he had to have someone else check out the indicator lights on computer hardware to see if it was showing ‘good’ or ‘bad’ indication.

    1.   This is not true. New Mexico has horizontal lights.  And a controlled intersection in New Mexico is sometimes a bar with 7, or more, lights depending on how many controlled lanes there are. I simply have no way to determine what to do at those intersections unless someone tells me.  No..  its not an non-issue..  Look at the lights in the following intersection and tell me which light is what color based on position..,+NM&hl=en&ll=32.869351,-105.968542&spn=0.058032,0.077162&sll=40.583257,-104.731894&sspn=0.05091,0.077162&vpsrc=6&t=m&z=14&layer=c&cbll=32.869396,-105.968735&panoid=5wR6kn85DhMbxfOBx0IrEg&cbp=12,315,,0,0

       I have the same problem that jrishel mentions below. I have a hard time spotting the traffic light itself in an urban environment with a lot of sodium traffic lights.

    2. As a friend of mine who is colorblind will tell you- horizontal lights will vary.


      Colorblindess varies not only in the colors, but in the degree of severity. A friend of mine (different friend) who is colorblind told me “color-confusion” is a better term. What red-green colorblindness meant to him was that red and green both looked the same or similar. A forest to him is always in autumn colors.

  7. I’m colorblind (protanopia) and usually use the order of the lights to figure out what’s going on, but at night, I sometimes have trouble distinguishing green traffic lights from sodium street lights, so end up slowing down when approaching a green trying to make sure I have a green light.  turning lights sideways does require an extra second for me to make sure I’m reading them the right way… and I think these shapes would take a bit to get used to.. it’d help if they added it to the vertical lights too.

  8. I’m with the others here: I thought the position of the lights was what gave the clue to the colorblind, which is also why road-signs have distinct shapes.
    And @boingboing-f1143e86b0f718851b742e7b0a1c5fe5:disqus a small number of people are truly colorblind, where they only see shades of gray, but most colorblindness affects just part of the spectrum.

  9. As I understand it the problem isn’t the regular lights, which they can tell by positioning but rather the 4-way  stop sign lights / amber caution lights that you find in some more rural areas because there is nothing to compare against.

    1. 4-way stop signs are an abomination. Roundabouts for everyone!
      (I grew up, and learned to drive, in Ireland and have lived in California for 10+ years)

  10. Clearly there are other ways for colorblind people to tell.  I think the point is helping them tell faster, which tends to be important while driving a car.

    In the US, we have both yellow flashing lights (exercise caution) and flashing red lights (treat as stop sign).  We typically use them sparingly, mostly during off-hours.

  11. Maybe shaped light are useful at night when you can’t clearly tell what light is on top, but I think that at night, with a bit of halo around the lights, it would be quite hard to tell if the shape is square, diamond or round…

  12. As others have pointed out, traffic lights are order red-amber-green from top to bottom (or in some countries also from left to right) for a reason.

    If you are close enough to distinguish the shape, you are probably close enough to see the position within the assembly. And at night the brightness of the lights will make determining the shape difficult as the darkness makes determining the position difficult.
    I think it is rather pointless. Having an illuminated border around the whole assembly would make way more sense to me as it would help colour-blind people in the darkness.

    And none of this is really accessible because you still need to be able to see … what about blind people? :-)

  13. It seems like a poor choice to make the green light the round one.  If someone gets used to thinking “round means go”, then encounters an old signal where the red is round, aren’t we all fail? 

      1. ‘Tis true, that’s nonsense in english, but it’s clear to anyone who speaks /b/.  The Internet has found its own uses for the word “fail”.  
        I used to resist it too, but, having not beaten ’em, I’ve joined ’em.

        1. I thought I understood the (mis)use of “fail” when it came to things like “packaging fail”, but I was honestly perplexed by “aren’t we all fail?” Then again, I never claimed to speak /b/.

  14. My town just got rid of their last light that was color blind safe.  It was a traditional red/yellow/green light, but in the light itself, it had blocked out Stop/Slow/Go on the glass.  It was a very old light and the only one in town like that, so now it’s gone…

  15. My colorblind dad from Michigan (where the stoplights were all vertical) had trouble the first few times he saw horizontal stoplights in California or in the south, because he didn’t know which position was supposed to represent stop or go or speed up. I don’t think the cop bought that excuse though. Still got a ticket.

  16. Typically, the single flashing lights are accompanied by other redundant signage, like for a flashing red, there would also be a stop sign, or for a flashing yellow, a crosswalk sign.

  17. @Paolo – If you think we American are being difficult about the Hague Convention on War Crimes, just wait until those UN guys try to force America to sign on to to the Vienna Convention on Road Signs and Road Signals.  Never, my Italian friend.  Never!

    (Also, I was always under the impression that the “green” was a bit more blue-green to avoid the colorblindness thing).

    @Colinadams – that’s true in cities, but a lot of rural highways hang them horizontally on the wires.

  18. As an engineer, this seems to me to be a simple and elegant solution to a problem that is apparently underappreciated by the non-colorblind public. I don’t go by the position of the lights, I go by the color- so lacking that information, a secondary clue would seem to be a good idea. The relative positions of the lights -left, top, whatever- don’t help drivers at night.

    A good design should also minimize the effects of basic human dumbness like putting streetlights and warning lights close to traffic lights. Even with normal color vision, I sometimes have difficulty figuring out which one is the traffic control.  Again, shapes would help us tell the difference.

    The masks shown are simple, cheap, and effective. Implent a shape standard and everyone will get used to it within a few months. As LEDs take over the traffic-light market, the red/yellow/green arrays can be fabricated in the shapes directly, further enforcing the standard as their incandescent ancestors pass into  history.

  19. In related colorblind news, my friend who’s colorblind tells me hunter orange looks exactly like foliage to him…..

  20. I’ve never been able to tell traffic lights apart from street lights or car headlights at a distance.  When they’re mounted in a vertical pattern I’m okay, but the horizontal mounted lights get me.  I’ve blown through red lights in New Jersey (the only place I’ve seen horizontal traffic lights), and only knew about it because my girlfriend started screaming from the passenger seat.

  21. The shapes are an interesting thought, but why would you want to introduce *new* shapes when you could use existing shapes that mean the same thing – ie – octagon = stop, triangle = yeild. These would move over very well to the shaped lights, then just use something else for green.

    Otherwise, the idea that an octagon AND square mean stop, and a triangle AND diamond mean yield contributes to visual information that may be confused.

    Also, if people become accustom to round meaning GO! then what happens to regular round traffic lights and signals? Do they all mean GO!

  22. As long as the “brightness” of each color is distinct, you can easily distinguish them despite color blindness.  To approximate: convert the colors to grayscale and see if you can still tell them apart.

    1. As long as the “brightness” of each color is distinct, you can easily distinguish them despite color blindness.

      Do you have any idea how difficult and expensive it would be to calibrate and maintain that, not to mention the effects of phenomena like snow?

  23. The main thing that gets me about traffic lights in the US is that they are mounted behind the intersection. Having been trained to drive in Germany, I have been conditioned to stop in front of the light (or the white line on the road more or less directly beside it). Driving in the US, I always have to concentrate to not do that, especially at night. And of course the horizontal lights so far high up are difficult too (the kind that is so prevalent in Texas).

    1. This is a state-to-state thing. In Wisconsin 99% of intersections have traffic lights before and after the intersection.

    1. The globally recognised stop sign is a circle with a diagonal slash. Even in America, everywhere except the DMV. Think GhostBusters :)

      A diagonal slash would seem more appropriate than something that’s indistinguishable from a circle at any distance.

      @boingboing-cb5eb6aa7ce2e4c6c2c11f8451c2f288:disqus : In each block of three colours, red is leftmost, green rightmost. At night… good luck. Only advice I can give is that if you drive through the intersection faster, I think you’re less likely to get sideswiped.

  24. Everywhere else?  You mean like Albania?  Turkmenistan?  The Isle of Man?

    1) The shapes of the lights are different: Red – square, Yellow – diamond, Green – round or arrow.

    2) In a lot of places in Canada, horizontal traffic lights will have TWO red lights; one on the left side, one on the right side.

    3) If you’re not colour blind, what do you care how the lights are arranged?

    1. If you’re not colour blind, what do you care how the lights are arranged?

      Welcome to the world of counter-empathy.

      1. Welcome to the world of counter-empathy.

        Would that be before or after someone T-bones you at an intersection. During the week, I bike to work and the school, so for me it’s not empathy, it’s self-preservation. However, I’m reasonably confident not all those people ignoring traffic signals are color-blind.

      2. So, like, in Quebec, deaf people are taught Quebec Sign Language, even the alphabet is different.  Anglophones in the rest of Canada are taught ASL.

        To me, this is stupid:  why would a subculture of a subculture (the roughly 55,000 QSL-signing Quebecois) want to limit their already limited field available for socializing?  Why not use ASL and have access to signers in the rest of Canada and all of the USA?   The various dialects of ASL aren’t an impediment and easily learned.

        However, I don’t get very exercised about it; it’s not my battle/place/onions (to use a French expression).  So call me counter-empathic to deaf people while you’re at it.

        The various solutions for the problem of colour-blind people and traffic lights seem to work for almost all colour-blind people – or so they tell us.  My daltonian father, who first pointed out the traffic light solution to me more than twenty years ago, told me it worked.

        So, again, why should non-colour-blind drivers care, eh, unless they’re control-freaks?

        1. To me, this is stupid:  why would a subculture of a subculture (the roughly 55,000 QSL-signing Quebecois) want to limit their already limited field available for socializing?

          They’re francophones.   Their social interests lie with the French-speaking world. 

  25. Some color blind people have difficulty telling what light is even when the sun is at a low angle. Shape would not help. My color blind co-work say he just make an educated guess. Scary!

  26. Actually it might make sense to have a secondary light to indicate the condition of the sign, especially at night.

    Have a white, non bright LED boarder around the whole sign.  So just a square if you will.  Have it steady with the green light, and flashing for the red and yellow.  It’d be relatively easy to see at night, and give a positional clue to which traffic color is lit up.

    1. I’ve seen, at one particular intersection in Northern Virginia, a red light that has a strobe tube across it which flashes when the light is red. Don’t know why I have never seen this anywhere else before, but it would work well here in San Jose, CA where the sodium vapor streetlights (they are used to keep down light pollution for the Lick Observatory) are often confused with red traffic lights.

      1. I’ve seen the strobe units before around the rural areas of NC.  I haven’t seen one in many years, so perhaps the strobe units died at a high rate or something.  The only irritating part about them was the strobe itself.  From far away it got your attention, but stopping at one, the strobe about blinded you.

      2. That intersection on Rt. 7 is known for dense fog (*and* has an eastbound lane) during the morning commute.  The flash in the red is to help warn drivers and draw their attention to it in spite of fog or the sun (hopefully…)

  27. I do agree with most people here on the vertical order of the lights.  I had a babysitter when I was 4 or 5 who was color blind (an older woman).  Occasionally we would go to the library and it was my job to help her with the lights.  It was like a learning game for me, and it gave her a little extra safety margin just in case.  Her only problem was coming up on a yellow, sometimes that took her a few seconds to figure out…

  28. My father is blue/green color blind.  In his eyes the grass and sky are just different shades of the same color.

  29. My father is Red/Green color blind and when I was only about 10 I asked him how he knew what the signal was. His answer was that he “knew the order”. The man has never had a traffic ticket over 40 years of driving so I take it that it has worked for him.

  30. One of my close friends is red-green colorblind. He goes by the position of the traffic lights, which always worked great for him until he visited Washington, DC. There, for the first time, he encountered traffic lights placed subtly on a pole at the corner of the intersection. Those looked like regular street lamps to him, especially at night. We had to yell “RED LIGHT!” a few times.

    Mind you, I have full color vision and I’ve still come close to running a few red lights when I drive in DC at night. I’m just not used to looking in my extreme peripheral vision for traffic lights.

  31. I have a very common form of red-green colour-blindness.  While traffic-light green doesn’t look green to me (usually it looks white or blue), it doesn’t look red or yellow. (And aviation green is even better – I easily distinguish aviation red, yellow, green, blue and white. The green looks blue, but it’s a different shade of blue from aviation blue.)

    Red/green single LED indicators, however, defeat me utterly. I absolutely cannot tell the colours apart without pulling out my handy-dandy assistive app (or back in the bad old days, my lighting gels). Canon projectors are the chief offender – when they show a blinking LED, I can’t tell whether it’s blinking red (shutting down), green (warming up) or yellow (change bulb) without some technological assistance.

  32. novel idea but that’s about it.  what’s wrong with what people have now — red on top, yellow in the middle and green on the bottom?  Color blind isn’t totally blind nor is it being mentally handicapped!  (Although I did have a boss once that was/is color blind and I considered him deranged!)

      1. Hmmm. “stop signs” aren’t “traffic signal” lights.  Someone must have hit you with a rock when you were looking!

  33. Silliest traffic-light thing I’ve seen in the US (TX at least) is the turn arrows. You have lit arrows, which is great, from an intelligibility point of view: you can clearly tell what they mean: “Turn here”. Or for the red ones, “Don’t turn here”.

    …except that they *change from red to green* when it’s OK to turn.

    Who thought that was a good idea?

    1. What? I don’t understand your confusion with turn arrows. When the arrow is red, you can’t turn. When it’s green, you can. What’s the confusion?

        1. In all the traffic signals I’ve seen with lighted arrows, the green and red arrows are in different positions from each other. How is that any more difficult than green and red discs in different positions?

  34. When you’re color-blind, people like to ask you “What color is this?” “What color is that?”  Then they squee.  They also think if they show you a color and say it slowly, you’ll suddenly be able to see it.  “This is blue.  BLUE. Got it?”

    Everyone who is color-blind sees colors differently; there’s no one single form of color blindness.  The lights in North America are fine due to positions as stated.  Also as stated, a single flashing light at a four-way intersection can be very confusing.  I always have to ask other people in the car if I have passengers what color the light is; unless I observe others either stopping or driving through it.

  35. Colour blind people: can’t remember that Top is Stop and Below is Go?

    Try to remember arbitary shapes! Much easier.

  36.  The way signals (each individual box of lights) in North America are supposed to work is that red is at the left (or top), and green is at the right (or bottom). If yours are backwards you should ask to have them fixed. I’ve never heard of red lights on both sides – two red lights at the left or top, yes, but not on both sides. Multiple signal boxes over the roadway, say one for each lane, is of course common if that’s what the commenter meant.

    I also wouldn’t agree that “most lights are vertical”. I’ve driven all over the western US and Canada, and I would say that most lights in the west are horizontal. Usually you see vertical lights for a left-turn lane. In older eastern cities like NYC, the lights are vertical. Could be an east-west thing?

    Lights at the far side of the intersection make sense to me. Driving in Argentina was a pain because we had to stop right under the light, and crane our necks to look straight up to see when it changed. How does that make any sense?

    1. “I’ve driven all over the western US and Canada, and I would say that most lights in the west are horizontal. … Could be an east-west thing?”

      I’m a lifelong Californian and have only seen horizontally-mounted traffic lights on out-of-state trips, generally around the South.

      I used Google Streetview to spot-check the downtowns of the largest cities in every Western U.S. state (AK, HI, WA, OR, CA, NV, ID, MT, WY, UT, CO, AZ, NM), and the only one to feature horizontally mounted traffic lights was Albuquerque. All the rest were vertical. It’s entirely possible that it changes by jurisdiction and other areas of these states could have horizontal lights. But a spot-check of large Western cities certainly suggests that vertical lights are more common than horizontal ones.

      1. Wow, I think you are right. I remember driving through e.g. Coeur d’Alene and it being horizontal lights, but they are vertical on street view.
        They’re definitely horizontal where I live, but maybe that just means Alberta is one of the handful of places where most lights are horizontal:

        1. I poked around Western Canada and saw vertical lights in Vancouver, Victoria, Saskatoon, and Winnipeg, horizontal lights in Calgary and Edmonton, and, weirdly enough, horizontal and vertical traffic signals at the same intersection in Regina.

          Okay, my curiosity got the best of me and I checked the largest cities in the rest of the U.S. states and Canadian provinces and territories. In the U.S., I found horizontally-mounted lights in the downtowns of Albuquerque, Houston, and Jacksonville (FL). Like Regina, I found a mix of both in Newark, NJ.

          In Canada, in addition to the above, I found horizontal lights in Whitehorse, YT and Charlottetown, PE. But not Halifax, where the picture at the top comes from. In Iqaluit, NU, there are no traffic lights, at least as of a couple years ago.

    2. I’m not saying it makes a lot of sense per se. Only that it’s a challenge if you have learnt driving with lights on the near side. In France, they have mini-lights at half-mast for the first driver to see. Now that makes sense to me.

  37. Speaking from personal experience, position doesn’t matter much at night.  The similarity of green to other street lighting is also a problem.  After a while you learn to distinguish these things pretty handily (by knowing exactly where to look carefully to discern the outline of the streetlight) but I was definitely at higher risk while learning to drive.  And probably still am, at least marginally.

    So yeah – traffic light accessibility: not quite there yet.

  38. Isaac Asimov made this question the centerpiece of his Union Club mystery, “Stopping the Fox,” originally published in the May 1982 Gallery — which, for some reason,* I have sitting around here, somewhere.
    * No doubt for “Hit the Road with the Hudson Brothers!” article it also containes. 

  39. For the traffic-signal wonks out there, it turns out that red and green signals aren’t pure colors:
    “Specifically, the CIE has addressed the problem of red-green confusers as follows: (1) The CIE green signal color is allowed to be sufficiently blue so that it is more readily distinguishable from red. This color is more blue than the ITE green.(2) The CIE red is limited to a zone that is more yellow than ITE red, allowing observers who have a reduced sensitivity to red to more easily recognize the color.”
    ITE = (US) Institute of Transportation Engineers
    CIE = International Commission on Illumination

    Charts of allowable color ranges at

  40. I’m Red-Green Colour blind.

    All of the colours can be very hard to tell apart depending on what time of the day it is. The only definite for me to tell them apart is based on the position. Red is always on the left or the top.

    How easy would it be to tell the shape of those lights from far away? They might just look like round shapes Or the green Go light.

  41. Tells you as much as top, middle, bottom or left, center, right.

    But then what about the blind blind? Oh how will they ever drive? The humanity!

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