Influencing Factor Analysis of Vehicle Emissions at a Signalized Intersection Based on Orthogonal Experiments

Considering the impacts of temperature and humidity, grade, medium-size vehicle ratio, bus ratio, and traffic demand on NO_x, CO and HC emissions of car, medium-size vehicle and bus, the orthogonal experiment scenarios were designed. Using the VISSIM software, the data of traffic volume, speed and the others were first obtained for each scenario. Then, the emission quantities and factors per link were estimated for different vehicle types and for different pollutants by combining the VISSIM software with the MOVES model. The analysis of variance and range analysis were carried out to process the outcomes from the orthogonal experiments, and the regression analysis was done to acquire the relationship between emission factor and grade. The emission factors at approaches and at non-approaches, and the emission factors obtained under various stages were also compared separately. The outcomes reveal that temperature and humidity, grade, medium-size vehicle ratio, bus ratio, and traffic demand all have significant impacts on vehicle emission quantities; the emission factor of each pollutant increases for each type of vehicle in non-congestion when the downhill grade declines or the uphill grade raises; the emission factors and their change rates with grade at approaches are 1.5-6.5 times higher than those at non-approaches; compared with stage three, the emission factors under stages four, five and six decrease by 27.5%, 38.8% and 54.9%, respectively. Results show that temperature and humidity, grade, vehicle composition, traffic demand, whether vehicles are at approaches, and emission stage all have important effects on traffic emissions for different vehicle types and for different pollutants.