3D crosswalk in Iceland helps slow down speeding motorists

Sounds like it'd work until everyone knows about it. What about an actual 3D object there (speed bump)?

Because a speed bump has a different purpose, and has some negatives associated with it (which is why you don't have speedbumps at every crosswalk). This should work even when people know about it, because the real point is to draw attention to the crosswalk. Probably the people who know about it, are less likely to hit someone in the crosswalk anyway, it's the people new to the area that are most likely to be dangerous.

Now if they put these everywhere, they'd stop losing their effectiveness.

I wonder how well it would work in the dark.

Well, if you can’t see the road, there’s a problem in and of itself. Assuming good headlights, which I think you’d want in Iceland, and assuming modern road paints, it should work. If not, just stick a road light over it.

There is an analogy here to the slippery-slope of attention-getting ads on the Internet. Once upon a time an ad was just a static (not even animated) banner of a certain size and shape. 468x60 was one of the earliest, IIRC. Advertisers invented new formats ("skyscrapers", "xl-leaderboards", "300x250", and so on), and also they got animated, and then they started expanding outside their areas, and so on; each new ad temporarily performed literally dozens of times better than the previous due to shock value.

A year or two after a new, more intrusive format became ubiquitous, its performance would fall back to the old format's, and, worse, the old format would fall even further because it was too subtle. So in the long run, the money would stay the same, but the pages got uglier, formats got crazier. The game theory is clear: everyone is incentivized to upgrade to the new formats, but once there, no one is better off (neither the publishers nor advertisers), and the readers themselves are far worse off.

We're seeing this now with traffic signals: if every crosswalk in the world is replaced with this 3D version, we'll see a temporary boost in safety, but in the long run it may return to normal and in my opinion, our world will be uglier. I don't like our public spaces covered in optical illusions.

In my area I've started to see red lights that are so bright you are temporarily blinded at night if you look at them. And they've even begun attaching strobing white LED's to the center of some of them. I would guess these perform great in short-term studies. Just like flash ads with games in them.