Determinants of Automobile Use

Germany and the United States have among the highest motorization rates in the world, yet Americans make a 40% higher share of their trips by car and annually drive twice as many kilometers per capita as do Germans. Automobile use is linked to unsustainable trends such as climate change, oil dependence, traffic fatalities, congestion, and obesity. Using two comparable individual-level national travel surveys, the study described in this paper empirically investigates the roles of socioeconomic and demographic factors, spatial development patterns, and transportation policies in explaining the differences in automobile use in Germany and the United States. In both countries, a higher population density, a greater mix of land uses, household proximity to a transit stop, fewer cars per household, and higher car operating costs are associated with shorter daily automobile travel distances. However, considerable differences remain: for example, Americans in settlements of more than 5,000 people per square kilometer drive as many kilometers as Germans in settlements with a density five times lower. A multivariate analysis shows that population density and automobile operating costs play roles in explaining differences in travel when controlling for socioeconomic factors. This is good news for the United States, because denser, more mixed-use developments and more automobile-restrictive policies can help increase the sustainability of the transportation system. In Germany, travel behavior is more homogeneous across all groups of society and in all spatial settlement patterns than in the United States. This is potentially related to historically higher gasoline prices and the greater availability of alternative means of transportation, which provide incentives for walking, cycling, and transit use.