2010 Progress Report: Framework for Context-Sensitive Spatially- and Temporally-Resolved Onroad Mobile Source Emission InventoriesEPA Grant Number: R834550
Title: Framework for Context-Sensitive Spatially- and Temporally-Resolved Onroad Mobile Source Emission Inventories
Investigators: Frey, H. Christopher , Rouphail, Nagui
Current Investigators: Frey, H. Christopher , Rouphail, Nagui , Xuesong, Zhou
Institution: North Carolina State University
Current Institution: University of North Carolina , University of Utah
EPA Project Officer: Chung, Serena
Project Period: May 16, 2010 through May 15, 2013 (Extended to May 15, 2014)
Project Period Covered by this Report: May 16, 2010 through May 15,2011
Project Amount: $500,000
RFA: Novel Approaches to Improving Air Pollution Emissions Information (2009) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
The objectives are to: (1) develop a robust, multi-scale methodology for estimating emission inventories (EIs) at various spatial and temporal scales; (2) evaluate the utility of meso-scopic and microscopic transportation models to predict vehicle activity at sufficient resolution and in analyzing future vehicle, control, or network design scenarios; and (3) quantify the relative contribution of vehicle type, vehicle activity, and traffic control measures on the magnitude and variability in regional emission estimates.
For Task 1, we have reviewed prior in-use emissions data collected from 2008 to early 2010 to create a "legacy" database of vehicle fuel use and emissions rates based on in-use measurements on selected routes using a Portable Emissions Measurement System (PEMS). Based on limitations of the existing data, we developed a study design for additional data collection as part of Task 3. We have collected measurements of additional vehicles as part of Task 4.
During the reporting period, the focus in Tasks 2 and 4 was on development and assessment of the utility of meso-scopic and microscopic transportation models to predict vehicle activity at sufficient resolution. This task required modifications to the meso-scopic model to enable the generation of synthetic vehicle trajectories, the expansion of traffic control measures, and the incorporation of vehicle operating modes (speed and VSP) into the simulator. The entire Triangle Regional Network has been implemented on a revised, open source and “lightweight” version of Dynasmart-P, called DTAlite. It inow is undergoing testing.
Based on a macroscopic kinematic wave propagation model, the open-source mesoscopic traffic simulation package first generates link-based vehicle-specific statistics and then uses a simplified linear car following model to construct second-by-second vehicle trajectories inside each link. The research team currently is using real-world vehicle trajectory data to examine the consistency between the macroscopic and microscopic traffic flow models, as well as the corresponding impact on multi-scale emission analysis. A novel model calibration method is developed to accurately estimate the stochasticity of microscopic car following behavior from second-by-second trajectory data, and the aggregated calibration results at the link level can provide a good foundation for macroscopic traffic models to capture time-varying traffic congestion evolution along freeway and arterial corridors.
Regarding the microsimulator, due to the finer resolution and processing time, the spatial focus was on a subnetwork of the Triangle region, and the objective was to assess the model validity at several scales, including macro (route) level and micro (second by second) vehicle activity. Both PEMS and fixed sensor data were collected for this task. Microscopic model assessment is virtually complete and will require modification of some model parameters, as described in this report. There has not been any change in goals, and the work is proceeding in a manner consistent with the research plan of the original proposal with minor modifications in the selection of the mesoscopic model for further development and dissemination.
As part of Task 6, we have developed a conceptual approach for a simplified fuel use and emission rate model that will be integrated with a Traffic Simulation Model. We conducted an evaluation of the concordance between trends in emissions rates predicted by EPA’s MOVES model and those observed in empirical data for passenger cars and passenger trucks, including variations with respect to driving cycles, vehicle age, and road type. Based on the results of this evaluation, we decided to use the MOVES model as the starting point for development of a simplified (reduced) form model, calibrated a simplified model, and evaluated it by comparing estimated emission rates to MOVES results for various driving cycles.
We will continue to collect field measurements of vehicles using Portable Emissions Measurement Systems (PEMS) to augment the legacy database and expand the sample of vehicles available for evaluation of the simplified fuel use and emissions estimation approaches.
During the next reporting period, one focus area in the micros-simulation arena will be an investigation of the model parameters in AIMSUN that could be altered to produce speed traces on arterials that better match real world observations. Assuming we are able to accomplish this task successfully, we will proceed with the validated model and approach (i.e., using driving schedule from model and VSP or MOVES for fuel and emissions estimation) to test several traffic control measures and assess their environmental impact at the route, link, and node level.
To further enable internally consistent cross-resolution traffic simulation, we plan to address the following three technical challenges:
- How to ensure that the simplified simulation model can reasonably and accurately represent traffic flow dynamics under different levels of car following driver heterogeneity?
- How to model multi-class traffic flow interactions at both macroscopic fluid and microscopic car following levels, as trucks and passenger cars have significantly different emission impacts?
- How to efficiently obtain macroscopic path-level network loading results that can be used to estimate region-wide traffic emissions, fuel consumptions for a wide variety of traffic management strategies?
We will add additional vehicles to the evaluation of the MOVES model based on comparisons to PEMS data. We expect to have data available for at least 10 additional vehicles during the second year of this study.
We will further develop, evaluate, and implement a simplified approach for estimating vehicle fuel use and emissions that can be incorporated into a Traffic Simulation Model.