The Canberra Cycling Promotion Fund demonstrated how much road space is required to transport 69 people by various modes. They used 69 people because that's the capacity of a Canberra, Australia bus. They used 60 cars because that's how many cars typically are carrying 69 people (1.15 people per car by my math.)
The idea came from a similar photo once made in Munster, Germany, explains Daniel Bowen in his blog, where I got the details since they are buried somewhere in the Canberra Cycling Promotion Fund web site.
I'm not sure if Mayor Marion Barry has seen the photo but apparently our governor got the message: