Take a close look at this picture. How many people are riding the bicycles? How much space do they take up? What is the density of bicycles per unit area on the road? How much space does the person driving the car take up? What is the density of cars per unit area on the road? How many cars would it take to fit the number of people riding bicycles on this road? How much space would these cars occupy?
Now head over here where the photograph is paired with an article. Guess what the author identifies as the problem in the picture.