Research On Coupled Mapping Model Of Urban Vehicle Activity And Emissions

Quantitive simulation of vehicle emission from urban transportation is not only a technical support for environmental impact assessment, but also a useful guidance to resolve the air pollution problem by urban and transportation planning. A lot of traffic information and tailpipe emission data were investigated in this study. To simulate vehicle emissions, a coupled model with two-stages mapping, general traffic information-driving bins-aggregated emission rate, was established. These model successfully connected traffic flow information with emission results. Relative emission rates were used to expanding the potential database for this model because of different characteristics in the on-board test versus the dynamometer test.Four cities were visited to investigate the traffic activity. According to investigation results, the identity of traffic activity was summarized by different urban clusters. Different cities have significant difference in static transportation information. However, the dynamic traffic activity shows comparability in some cities. Beijing, Shanghai and Istanbul have similar vehicle driving characters on same kind of roads. Domestic cities, including Beijing, Shanghai and Tianjin have similar hourly variation of driving and starts, which is quite different from Istanbul. Based on domestic traffic activity, totally 39 traffic patterns were established to simulate the vehicle activity in mega-cities in China. Then an effective approach, mapping the vehicle activity bins based on the macro transportation information, is proposed. The differences on vehicle stock, vehicle type and traffic flow distribution between the two inventories (tested and simulated) are less than 10%.Besides this, on-board instruments were used to test the tailpipe emissions from diesel trucks. Great improvements for gaseous pollutants and Particulate Matters (PM) are found between Euro 0 and Euro I Xi'an trucks and between Euro II and Euro III Beijing trucks. NOX emission did not show a trend of reduction. The urban or rural driving mode resulted in an up to 200% increase in pollutants compared with highway driving. Emission per distance traveled is higher in Beijing than in Xi'an while emission per kilogram of fuel consumed is lower. Totally 30 bins in three groups are used to calculate emission rates in aggregate model. The emission rates keep growing in the first five bins in each group and the growing rate increased from group 1 to group 3. Clusters and multivariable linear regression models were combined to develop a micro-emission model. Both the aggregated and instantaneous emission results showed that the model tracked the measurements results well. The aggregate model was established beside the micro-emission model. Based on relative emission rates, emission database from dynamometer are used to set up the secondary mapping for passenger vehicles, buses and trucks.The coupled model with two-stages mapping is used to simulate vehicle emissions during Beijing Olympics. The simulation results of traffic volume, average speed and frequency distribution of driving bins are close to tested results, while the difference is less than 20%. The difference for key factors is less than 5%, such as the average speed on arterial and highway, and the frequency on high emission bins. Simulation results show that the total reduction of HC, CO, NOX and PM from buses, taxies and cars reached 59%, 65%, 42% and 24%.