The first traveler decision to be modeled in the sequential approach to travel demand and traffic forecasting is trip generation. The objective of trip generation modeling is to develop an expression that predicts exactly when a trip is to be made. This is an inherently difficult task due to the wide variety of trip types (working, social/recreational, shopping, etc.) and activities (eating lunch, exercising, visiting friends, etc.) undertaken by a traveler in a sample day. To address the complexity of the trip generation decision, the following approach is typically taken:
1. Aggregation of decision-making units. Predicting trip generation behavior is simplified by considering the trip generation behavior of a household (a group of travelers sharing the same domicile) as opposed to the behavior of individual travelers. Such an aggregation of traveler
decisions is justified on the basis of the comparatively homogeneous nature of household members (socially and economically) and household members’ often intertwined trip-generating activities (joint shopping trips, etc.).