From the summary:
This report examines the key differences and determinants of travel behavior in Germany and the United States. Americans travel by car twice as much per year as Germans and use transit only a sixth as much. Differences in car reliance between the United States and Germany are not solely due to income or residential density. Germans in the highest income quartile make a lower share of their trips by car than Americans in the lowest income quartile. And Germans living in low density areas travel by car about as much as Americans living at population densities five times higher.
The result is a transportation system in the United States that is less sustainable than in Germany. The per capita carbon footprint of passenger transportation in the United States is about three times larger than in Germany. Although gas prices in the United States are half those in Germany, Americans spend five percent more of their budgets on transportation than Germans. In government outlays as well (federal, state and local), Germany spends less per capita on transportation than the United States.