External Trips Module

The external trip module is responsible for synthesizing truck travel movements from spatially exogenous agents which are crucial for accurately reflecting traffic conditions at the boundary of the model and accurately reflecting the overall regional traffic congestion. This module synthesizes three types of external truck trips (1) internal-external (IE) trips, (2) external-internal (EI) trips, and (3) external-external (EE/pass-through) trips. The module incorporates three main procedures: data processing, disaggregation, and calibration. It should be noted that currently only EE trips are utilized downstream in POLARIS from this module, as both IE and EI trips for simulation are now being produced endogenously by the freight ABM framework. IE and EI trips synthesized from this module is only for calibration purpose. FAF5 data is used to provide external truck tonnage flows and zone boundaries for truck flow disaggregation, as well as link and node locations for finding paths. Data processing involves two main tasks: identifying the entry and exit links on the boundary of the study region, through which external trips must pass; and identifying an outer boundary of the study region, within which FAF zones are disaggregated to counties by better identifying the origins and destinations of passing-through trips outside the study region. The second component disaggregates FAF5 truck tonnage data from the FAF zone level to the county level using gravity models, with flow attractions and productions adjusted based on county-level employment. The tonnage flow is also converted to truck flow by considering the share of empty trucks. In the third component, the friction factor function parameters in the gravity model, empty trip parameter, as well as the function for attraction and production adjustments, are calibrated to estimate empty trips and minimize deviations of both loaded and empty flows compared to link flows on the Highway Performance Monitoring System (HPMS). The link-to-link truck flows are further tagged with the nearest POLARIS location-to-location truck trips as the final input for external truck trips.

Important

Please refer to the the following papers for more details:

Ismael, A., Y. Huang, H. Shen, and O. Sahin. Modeling External and Empty Freight Truck Trips Using Agent-Based Simulation. Procedia Computer Science, Vol. 238, 2024, pp. 791–796. https://doi.org/10.1016/j.procs.2024.06.093.

Huang, Y., A. Ismael, H. Shen, O. Sahin, and P. V. de Camargo. External Truck Trip Synthesis and Calibration for Regional Freight Simulations. Presented at 104th Transportation Research Board Annual Meeting.