Daily Roadside Math

Walking around Vancouver today I noticed this stretched bicycle sign:

Why is it so distorted? Was it painted by a machine that accidentally accelerated shortening the bicycle at the top?

There must be a reason for this distortion. Probably something facilitating our perception. Similarly to the Ambulance sign painted with a horizontal flip on the ambulance truck to allow the sign be correctly read in a rear view mirror.

Let's see. Who is it for? A warning for approaching cars and bicycles that this road is bicycle only. They should be able to see it from 20-50 feet away. Let's check how the sign looks from such distance:

Just perfect!
What exactly is happening with this visual illusion?
The drawing of the bicycle is cleverly made to account for the perspective projection distortion in our eyes (and brain) and allows for the bicycle to be perceived clearly from the average height and far distance. Note how the bicycle wheels appear perfectly round on the second picture.

This is simplified demonstration of our eye perceiving bicycle wheel as perfectly round from a distance and as an oval from close up.

Now, how about an explanation to this signage?


  1. Hey Math Mom! Since you're the queen of everyday math, I thought you might appreciate this video: http://www.alleyoop.com/blog/2011/09/07/everyday-math-video-using-math-skills-on-the-street/

    Talk to you soon. - Hannah

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