Urban Diesel Bus Emission Modeling And Its Application

Urban diesel buses are the major contributors to the total emissions of the urban road network due to the larger displacement, frequently-changing driving cycle, long driving time and bad quality of the fuel. The accurate estimation of the bus emission should be based on the emission models, and then the results can be used to reduce pollution. However, there are no suitable diesel bus emissions models that can be used to estimate the emissions generated near bus stops, intersections and links during the real-word driving in China.So in order to establish the urban diesel bus emission models, the Portable Emission Measurement System (PEMS) was used to collect the real-world instantaneous data of bus emissions. Then the factors can be found out which influence the emissions generated near bus stops and links. Finally, the bus emissions models can be developed and applied to solve real traffic problem.First, the PEMS tests and the related traffic surveys were described in detail. Then a summary of simulation data and the data processing were discussed. Based on the instantaneous emission, driving data and related characteristics of bus stops and intersections, the influence of each factor on diesel bus emission was analyzed. At the same time, an empirical method was demonstrated to evaluate the emission near bus stops and explore emissions characteristics near bus stops. The results show that VSP which contains the information of vehicle speed, acceleration, vehicle mass, and road grade is identified as an explanatory variable which is highly correlated with emissions. In addition, it is also found that the influence of passenger load can be omitted in the emission rate models at low and medium speed bins but has to be considered in the models for high speed and VSP bins. Otherwise it could lead to an error up to 49%.Second, the diesel bus emission calculation mode and regression models were developed based on the analysis of influence factors. In addition, the calculation method of distance-based emission factors was put forward after model validation. Then a method to assess the environmental impact of signalized intersections was discussed using the real world emission and delay data near intersections. Moreover, the relative ratio of emission factors was calculated to represent the environmental impact of intersections. Last, the micro traffic simulation was combined with the emission models. Simulation of the traffic environment at bus stops or intersections will provide inputs for emission models. The bus fleets emissions at intersections can be forecasted and then the potential benefits of bus priority strategy in terms of emissions can be investigated. The results showed that the strategy was useful to reduce the bus fleet emissions but it may bring the negative effect to the total emissions of the road network.Finally, the framework of urban bus emissions analysis system was developed based on ArcGIS. The system consists of three sub systems, a user-interface subsystem, a database subsystem and an emissions estimation subsystem. And furthermore, the results can be applied to the Advanced Public Transportation System to achieve the visualization of bus emissions in real time.