Assessing Micro-Scale Carbon Dioxide (CO2) Emission on UK Road Networks using a Coupled Traffic Simulation and Vehicle Emission Model

With an increasing divergence between test certified vehicle emission and on-road vehicle emission, the accurate appraisal of real-world vehicle emission has arguably never been more important. This research advances the development, calibration and validation of a coupled traffic micro-simulation and instantaneous emission model. A portable emission measurement system (PEMS) data set was used to quantify the real-world CO2 emission of a passenger car through an urban traffic network, in Leeds (UK), over the diurnal range of traffic flow conditions. Utilising these data, analysis was conducted to assess the accuracy of CO2 micro-scale emission estimates by four emissions models; the Emissions Factors Toolkit (EFT), the Handbook Emission Factors for Road Transport (HBEFA); the Motor Vehicle Emission Simulator (MOVES); and the Passenger car and Heavy duty Emission Model (PHEM). The results demonstrated the strength of power based models over average speed based methods. The study identified the influence that road grade can have on the micro-scale modelling of exhaust CO2 emission and developed a novel methodology to incorporate grade into the modelling. A coupled traffic simulation and instantaneous emission model was developed for the study area, using the simulation tool AIMSUN and the emission model PHEM. The model was separately calibrated and validated for five time periods. Parameters within the coupled model, such as the vehicle fleet and vehicle dynamics were customised for the specific study area and time period. The research demonstrated the ability of the AIMSUN-PHEM model to deliver an accurate appraisal of on-road CO2 emission for each time period and its capacity to generate a range of emission factors from those of a single vehicle to those of the entire fleet. This work confirms that a properly calibrated traffic simulation emission model can provide an effective method for conducting high resolution analysis of vehicle emission in a network.