AN ENDOGENOUS SWITCHING SIMULTANEOUS EQUATION SYSTEM OF EMPLOYMENT, INCOME, AND CAR OWNERSHIP

The research presented here makes an advance toward the inclusion of e mployment and income within a transportation framework based on the co nceptual framework developed by the authors in a preceding paper. Empl oyment and income are important determinants of travel behavior. They have been used as exogenous variables in travel forecasting models suc h as trip generation models, car ownership models and mode choice mode ls. This paper proposes a fundamental change in the current view of em ployment and income as exogenous variables in travel demand models. In particular, we emphasize the need, both from a forecasting and estima tion point of view, to include employment and income as endogenous var iables within a disaggregate travel demand modeling framework. The pap er formulates and estimates an integrated model of employment, income and car ownership, which takes account of interdependencies among thes e variables and their structural relationships with relevant exogenous variables.