Walking, Cycling, and Obesity Rates in Europe, North America, and Australia - Walking and bicycling are far more common in European countries than in the United States, Australia, and Canada. Active transportation is inversely related to obesity in these countries. Although the results do not prove causality, they suggest that active transportation could be one of the factors that explain international differences in obesity rates.
Making Transportation Sustainable: Insights from Germany (PDF file) has many interesting insights and comparisons between the U.S. & Germany: "Increasing transportation sustainability in the United States requires policies that foster changes in travel behavior. Germany’s case may provide a helpful example. Although car use has grown in both countries, Germany has been far more successful than the United States in creating a more balanced transportation system."