Donald Appleyard drew that conculsion in his 1981 book, Livable Streets, which was based on studies he conducted in the late 1960s in San Francisco. Appleyard, a former University of California, Berkeley professor who passed away in 1982, found that people tended to connect more with their neighbors, socialize and feel a sense of ownership and pride about their neighborhoods on streets with lighter traffic.

A person on a light traffic street had an average of three friends, while a person on a heavy traffic street had an average of 0.9 friends. The Streetfilms video shows how heavy traffic streets seems to impede the flow of people from one side of the street to the other, limiting their access to friends and socializing opportunities.

"The fact that the amount of traffic on the street on which you live can impact the number of friends you have in the world is an enormous significance," says Mark Gorton, executive director of Open Plans in the video.

Appleyard's work has recently been shored up by findings by United Kingdom researcher Joshua Hart.

Livable Streets is set to be republished in 2011.