Center for Activity Systems Analysis

A trip generation model has been developed using a time-use perspective, in which trips are generated in conjunction with out-of-home activities, and time spent traveling is another component of overall time use. The model jointly forecasts three sets of endogeneous variables -- (1) activity participation and (2)travel time (together making up total out-of-home time use), and (3)trip generation -- as a function of household characteristics and accessibility indices. It is estimated with data from the Portland, Oregon 1994 Activity and Travel Survey. Results show that the basic model,which has ten endogeneous time use and trip generation variables and thirteen exogeneous variables, fits well, and all postulated relationships are upheld. Tests show that the basic model, which divides activities into work and nonwork, can be extended to a three-way breakdown of subsistence, discretionary and obligatory activities. The model can also capture the effects of in-home work on trip chaining and activity participation. We use the model to explore the effects on time use and trip chaining of GIS-based and zone-based accessibility indices.