Future Household Transportation Demand: A Comparative Analysis of the U.S. and Austria

Alexia Fuernkranz-Prskawetz, Max Planck Institute for Demographic Research
Leiwen Jiang, Peking University
Brian C. O'Neill, International Institute for Applied Systems Analysis (IIASA)

Understanding the factors driving demand for transportation in industrialized countries is important in addressing a range of environmental issues including local air pollution and climate change. Understanding is also an aid to planners who must anticipate infrastructure needs and address congestion concerns. Research on travel demand and transportation fuel use has shown that demand generally rises with income. Non-economic factors have received less attention but have been found to be important. Links between indicators of lifestyle and energy use have been identified. Analyses of household survey data in the U.S. have shown differences in travel demand across households that differ in the age and gender of the householder, household size and composition, and family type. Other studies have shown that household characteristics are not only important in explaining variation in travel demand, but also in anticipating household response to price changes or other policies. Little work has focused on the role demographic characteristics of households might play in explaining past changes in aggregate demand, or to predict future changes. Scenarios for future transportation demand have been hampered in particular by a lack of detailed, long-term household projections. We analyze how future demographic trends could affect household transportation demand in two industrialized countries: Austria and the U.S. Based on detailed household projections, we demonstrate that the two countries are likely to experience distinctly different trends in population composition by some household characteristics. For example, while a continuation of recent trends would lead to a continued shift to smaller households in Austria, the household size composition of the U.S. population remains approximately stable in a reference scenario. In other ways future trends may be more similar: both countries will see rising proportions of households headed by the elderly, and household distributions will be affected in similar ways by the aging of the baby boom generation. We examine the implications of these demographic trends for transportation demand by combining the household projections with cross-sectional data on household car use. In both cases, results depend on the compositional variables included in the analysis, emphasizing the importance of careful model selection. Results also demonstrate that differences in underlying demographic factors are likely to require consideration of different models: while changes in household size may not be a strong determinant of travel demand in the U.S., it will be important in Austria. In both countries, disaggregation of households by age of householder appears to be important to capture the effect of the baby boom generation passing through different stages of the lifecycle associated with sharp differences in transportation demand. Incorporation of these demographic effects can produce significant difference in anticipated demand over the next few decades, relative to scenarios that do not consider changes in demographic composition.