To compare regional energy use and emissions across travel modes, analysts need to have detailed trip-level information on mode, trip distance, and trip duration, as well as the on-road operating conditions that affect vehicle energy use and emissions. Vehicle occupancy further complicates comparative analyses across modes. Most travel demand models retain information about each single-occupancy vehicle and carpool trip (by vehicle occupancy), but origin-to-destination paths that allow more detailed energy use and emissions assessment are not retained. Regional models also do not predict transit vehicle occupancy (transit vehicle boarding is never compared to transit vehicle capacity), nor do the models retain transit trip paths that could be used in energy and emission analysis. These modeling limitations force analysts to use average speeds over entire trips and broad vehicle occupancy assumptions in comparative energy and emissions analysis across modes.
The Georgia Tech research team will integrate modeling tools and data to support detailed comparisons of energy use and emissions across transportation modes on a per-passenger basis, using travel demand model outputs for the Atlanta metropolitan area. The team will integrate: 1) automobile trip path retention model enhancements recently developed by the team for the Atlanta Regional Commission’s activity-based travel demand model (ABM2020); 2) transit path prediction routines from TransitSim, which was developed by the team using GTFS data feeds for regional transit routes and schedules; and 3) MARTA-monitored occupancy data by transit route and time of day, based upon transit fare card capture data. The path retention routines allows users to estimate energy use and emissions on each transportation link using the MOVES model and Fuel and Emissions Calculator (for rail trips), rather than using average speeds over an entire trip. The regional model already tracks automobile travel by vehicle occupancy mode (SOV, HOV2, HOV3), and the new MARTA data will allow modelers to much more reliably estimate energy use and emissions on a per-passenger basis on each transit and roadway path. Once the system is completed, energy use and emissions per-passenger can be compared in time and space, across modes, on any corridor, by trip purpose, for any origin-destination pair, etc.