This study explores the aggregate causal relationships between telecommunications and travel in a comprehensive framework, considering their demand, supply, and costs, together with land use, economic activity, and sociodemographic variables. On the basis of a hypothesized conceptual model, composite indexes were developed for endogenous variable categories (telecommunications and travel demand, supply, costs, land use, and economic activity) by confirmatory factor analysis, with the use of national time series data (1950-2000) in the United States. Then, single-equation and structural equation models for telecommunications (telephone calls and mobile phone subscribers, separately) and travel were estimated, with the composite indexes and sociodemographic measures used as explanatory variables. Overall, the model results suggest that the aggregate relationship between actual amounts of travel and telecommunications is complementarity, not substitution. That is, as telecommunications demand increases, travel demand increases, and vice versa. In addition, it was found that the causal effects of travel demand on telecommunications demand were larger than those in the reverse direction.