A Simulation And Optimization Study Of Urban Road Traffic Emissions

With the rapid expansion of urban size and increase of number of automotive vehicles, road traffic emissions have already been the main source of atmospheric pollutants in many metropolitan areas. The issue of traffic environment is becoming one of the most severe challenges for the sustainable development of urban transportation system. How to control and reduce traffic emissions in order to improve traffic environment has attracted more and more attention from researchers and traffic decision makers.Vehicle emission models are effective tools that are used for calculating vehicle emissions. Traffic simulation models are mathematical models used to study traffic behavior and the changes of traffic movements over time and space. At present, the integration of vehicle emission models and traffic simulation models has becoming one of the most effective methods of studying traffic emissions. Based on detailed analysis of the domestic and foreign development trend in the research area of traffic emission, this dissertation chose CMEM, an American microscopic emission model, as the study tool of calculating vehicle road emissions and performed parameter calibration and model validation using real world measurements collected in China. In addition, a real road intersection in a Chinese city was coded in VISSIM, a German microscopic traffic simulation model, and the driving behavior parameters was also calibrated using real traffic measurements. By coupling the calibrated CMEM model and the calibrated VISSIM model, this dissertation evaluated the current traffic flow parameters and traffic emissions. Further, the effectiveness of different optimized traffic signal plans in improving traffic flow and reducing traffic emissions was studied.The main study works in this dissertation are listed as follows:(1) Collection and post processing of vehicle on-road emission measurements;An experiment scheme was designed based on the on-road emission measurement system OBS-2100 to collect real world emission measurements of Chinese urban vehicles. After post processing of these data, a database of Chinese vehicle on-road emissions was developed using MySQL. (2) CMEM parameter calibration and model validation;Based on detail analysis of model structure and calculation principle, several calibration parameters of CMEM model were selected. A "two-stage calibration approach" was proposed for these calibration parameters using "grid search" method" and "nonlinear simplex" method. Then, the CMEM model was calibrated and validated using the real world measurements collected in China, which makes it estimate the on-road emission level of Chinese vehicles more accurately.(3) VISSIM modelling and parameter calibration;The study intersection was coded in VISSIM based on collection of a large amount of traffic measurements by a traffic survey test. The related driving behaviour parameters in the VISSIM model were calibrated in accordance with a parameter calibration flowchart proposed in this dissertation. In addition, the estimation accuracy of the calibrated model was validated by real measurements.(4) Evaluation of traffic flow parameters and traffic emissions and optimization of traffic signal control strategies.The reasons that traffic management and control strategies can help reduce traffic emissions were analyzed based on the analysis of main impact factors of vehicle on-road emissions. Traffic flow in the study area was evaluated by VISSIM simulations and the current traffic emissions were calculated by CMEM model. In addition, the current fixed stage signal plan was optimized using genetic algorithm based on different optimization objective functions (average traffic delay and average number of stops). Traffic flow and traffic emissions were compared before and after the traffic signal optimization. Further, a vehicle actuated signal plan was developed for the study intersection and the vehicle actuated control parameters were determined by genetic algorithm optimizations. Finally, the effectiveness of optimized fixed stage signal plans and optimized vehicle actuated signal plans based on different objective functions in improving traffic flow and reducing traffic emissions were compared and analyzed.