Modeling External Trips: Review of Past Studies and Directions for Way Forward

AbstractProper estimation of external trips is vital because it may affect the model validation results when compared with traffic counts. In practice, external trips are divided into three categories: external–external (EE), external–internal (EI), and internal–external (IE) trips. EE and EI trips are carried out by nonresidents, whereas IE trips are carried out by residents of the study area. This paper discusses modeling attempts for EE and EI trips and the application of existing models for generation and distribution of EE and EI trips. These models are applied in the Leuven region of Belgium to study their transferability, which was found to be poor. Given these shortcomings, new extensions and variables are proposed that have improved the model performance. Then, the current practices to incorporate residents’ external trips (IE) in activity-based models are also described along with their consequences in the demand modeling framework. An approach by defining a catchment area (CA) outside the study area is then proposed to improve the modeling framework. Results validate the proposed methodology. The paper, therefore, shall be beneficial for both researchers and practitioners.