It is frequently assumed that a relationship exists between urban form and travel behavior. As distances are not travel choices in itself, but the consequence of other decisions, this paper tests, consistent with the activity-based approach, a causal model that does not relate urban form directly with daily travel distance, but indirectly through a series of decisions. For this purpose a structural equation model is developed to simultaneously estimate direct and indirect causal relationships. Urban form is included as urban density for the residential environment and a measure for mix and density for the work environment. Case study is the Randstad in the Netherlands. The model confirmed the hypotheses from activity-based theories that activities are derived from needs and preferences that are related to household and location choices; moreover, travel decisions are taken from activity participation; travel time and distance result for the greater part from these decisions. Effects from residential density suggest that people in a dense residential environment travel a little less, although this effect is partly canceled out by extra activities. Workplace density indicates that workers in higher densities make more extra trips. Results show a reducing effect of the daily distance traveled by car for both urban form of the residential and the work environment. The model also demonstrates, however, that indirect effects can steer a total effect in another direction, indicating that the apparent effects of one variable on another can be the trade-off of opposite effects.
Abstract