Each of these buses is proceeding smoothly along the striped street. Yet each seems to be varying its speed dramatically.

When the blue bus encounters a white stripe, it becomes easy to see due to the high contrast, so it appears to move faster. When it encounters a black stripe it becomes harder to see, so its movement seems slower. The reverse is true of the yellow bus. When the stripes are removed, the buses stop staggering.

UCSD psychologist Stuart Anstis first demonstrated the illusion in 2003.