Why have Danes again been named the happiest people on the planet? Early this year ABC News cited bikes as "perhaps … the best symbol of Danish happiness," and in this clip from "Contested Streets" it isn’t hard to see why. Here, livable streets guru Jan Gehl and others explain the many ways an increase in bike traffic (now one-third of all commutes) has improved life in the capital city of Copenhagen.

But it didn’t happen overnight. Rather, it took four decades of gradual change to make Copenhagen the place it is today. As for replicating that success elsewhere, says Gehl: "if you don’t have enough nice spaces, you can see these [become] overcrowded spaces. Then you should just make more spaces."