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I noticed that too. I think it's because the buses are 3 stripes long instead of 4.

After I changed the "--bus" CSS variable from 30px to 40px, I got the stepping effect.

That's really fascinating. Multiples of 20 give the stepping effect, while the other offsets of 10 grow and shrink. Stuff in between do a strange shrink and stop and grow. I thought 20 looked the best though.

I always loved making web remakes of common GIF illusions [0] where you can mess with variables and see what impact it has. This is a perfect example of that.

[0] https://ehsankia.com/cjs/#19

This makes some sense: to maximize the illusion, both leading and tailing edges of the bus should be going through the light and dark strips at the same time.

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