NAtional Vehicle Itinerary GenerATor (NAVIGAT)

In this study, a large-scale passenger vehicle mile travelled (VMT) simulator, called NAtional Vehicle Itinerary GenerATor (NAVIGAT), is developed to simulate household-owned passenger vehicle movements within the whole U.S. at census tract level resolution (including all 50 states and Washington D.C.). NAVIGAT adopts a modeling framework resembling the traditional travel demand models that are often applied in a regional context, combined with a datadriven approach that estimates model parameters using various national-level data sources. Using NAVIGAT, vehicle movements can be tracked throughout the network at the census tract level, and used to track utilization of specific vehicle types or technologies given a technology adoption scenario input, also mapped to the census tract level. NAVIGAT outputs can support the estimation of key transportation and environmental metrics, including location-specific changes in on-road emissions, and subsequent air quality and health impacts on nearby communities. These changes may result from shifts in technology adoption driven by factors such as the deployment of charging infrastructure, adoption incentives, and fluctuations in fuel or vehicle prices. 

Data and Methodology Overview 

A previously developed national-scale geospatial typology is adopted to capture the spatial variability of travel demand across the nation, and to generate vehicle flows under various transportation scenarios while maintaining a reasonable computational speed. The major functionalities developed in NAVIGAT are illustrated in Figure ES-1. The observed travel demand is generated from 2017 National Household Travel Survey (NHTS) data and aggregated by geospatial typology for national application and imputation for census tracts without observed data. The demand generation rate is multiplied by the American Community Survey (ACS) population to generate total demand at the census tract level. The travel demand is distributed across the entire network using destination choice and route selection models. The fractions of flows are used to split observed “through” traffic—travel that occurs in tracts outside the origin or destination tract of the trip—to corresponding home locations. Both in-state travel and cross-state spillover travel are modeled in NAVIGAT, and calibrated to align with observed daily VMT from Highway Performance Monitoring System (HPMS) data.