Using optical illusions as traffic regulators

I love optical illusions and this one in Iceland (that I came across thanks to Richard Kaufman) seems to suggest a pedestrian crossing that is floating on air. But it is not just for fun. Such trompe l’oeil (“fools the eye”) illusions claim to have the benefit of causing drivers, puzzled by what they see ahead of them, to slow down when approaching them, increasing the safety of street crossers.

I am not so sure about this. It seems to me to have some serious downsides. The first is that drivers who encounter them for the first time might slam on the brakes in alarm, causing rear-end collisions. Another is that once drivers know it is an illusion, they may just start to ignore them and breeze through as before. Here is a video of the above crossing and at the 59 second mark, a van sped through the above crossing without slowing down. The driver, in addition to not being courteous to pedestrians, must have been that way before.

The third is the most dangerous and that is the inverse of what is being sought, that too many such illusions might cause drivers to think that something real is an illusion and ignore it, and that could be fatal for illusions like this child running after a ball in the street.

If I encountered this illusion, I would definitely stop, risking being rear-ended. Even after I realize that it is an illusion, it would make me queasy to drive over it. It would just seem wrong.

You can read more about the use of such road visual illusions for road safety purposes in this article.

All in all, I think it is dangerous to make drivers unsure of what is real and what is an illusion.


  1. says

    It’s a bit misleading to blame the driver for going through without slowing down when there were no pedestrians in the crosswalk at the time.

    I used to have neighbours with a pair of red lights in their yard, next to the roadway, to make people down. Whenever visibility was limited they resembled brake lights and gave the false impression that the road was straight rather than curved. People would drive into their yard in the fog or snow thinking that they were following another vehicle on a safe path.

  2. chigau (違う) says

    The floating crosswalk would work for me.
    A visual cliff would be more effective than the little girl.

  3. Holms says

    I have heard of car parking buildings trialling illusions resembling hovering writing saying “SLOW” and similar, only to have to cancel the trials early due to increased car accidents caused by startled drivers.

  4. Owlmirror says


    It’s a bit misleading to blame the driver for going through without slowing down when there were no pedestrians in the crosswalk at the time.

    But a purported effect of the illusion in front of the driver is that it supposed to cause the driver to slow down from confusion at what they’re seeing.


    I tried searching for driving rules in Iceland (specifically, whether it is required to slow down at pedestrian crossings), and couldn’t find anything. Most of what is available seems to be written under the assumption that the driver will be on the ring road touring rather than driving in urban areas. The closest I could find:

    The general speed limit is 50 km/h in urban areas, 80 km/h on gravel roads in rural areas, and 90 km/h on asphalt roads.
    Please note: special warning signs indicate danger ahead, such as sharp bends, but there is generally not a separate sign to reduce speed. Please choose a safe speed according to conditions.

  5. Owlmirror says

    Here’s a page with more information about the 3-D crossing:


    But as Trylla tells Quartz, he has noticed a difference: “What is clear so far is that it has received a lot of attention and people are for sure driving differently over this crossing, even if they’re eventually getting used to seeing it. So in that way, I would say that it’s a success so far.”

  6. Owlmirror says

    OK, one more link:

    Ralf told Vísir that in the narrow residential streets in the old village in downtown Ísafjörður a speed limit of 30 kmh (18.6 mph) is simply too high, and other ways must therefore be found to slow motorists down even further.

    So it’s not just a desire to slow down traffic approaching the crossing, but a desire to slow down traffic on the narrower streets of the town in general. But apparently, they don’t want to reduce the legal speed limit on those street (and inflict fines on those going faster) — just encourage slowing down.

  7. EigenSprocketUK says

    A trompe l’oeil like this will only work from one direction. Maybe they are only trying to discomfit drivers entering town from a faster road.
    And, once you get closer, the illusion disappears. This could be good because the driver is now free to concentrate on the other road users instead of the crossing. Or it could encourage drivers to avert their attention from the far+mid distance and solely concentrate on the short distance. Obviously such a focus on only the close proximity is bad (but worryingly common with inexperienced drivers and tired drivers who haven’t yet realised they’re tired.

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