Improved Vehicle-Specific Power Bins for Light-Duty Vehicles in Estimation of Carbon Dioxide Emissions in Beijing

With increasingly wide recognition and acceptance of vehicle-specific power (VSP) as a viable variable in modeling vehicle emissions, the method for defining VSP bins is becoming critical. The primary objective of this study is to develop emission-specific VSP bins for estimating carbon dioxide (CO₂) emissions for light-duty vehicles by using the real-world data collected in Beijing. The proposed method is developed by considering both emission characteristics and emission contributions of each bin. In this method, speed is chosen as the secondary parameter in defining bins because it has a higher impact on the CO₂ emission rate than the engine stress for each VSP bin. With the proposed method, 24 VSP bins are eventually defined on the basis of the emission data collected in Beijing. In the proposed VSP bins, the data under VSP < 0 are grouped into one single bin because of their similar CO₂ emission rates and comparable total emission contributions to other bins. Data at VSP = 0 are defined as an independent bin for characteristics that this single VSP point carries, such as its high VSP frequency, high total CO₂ emission contributions, and significant lower emission rate than that of adjacent bins. On the basis of the validation of the proposed method, it is found that the use of an independent bin for VSP = 0 improves the accuracy of CO₂ emission estimates and that the use of a single bin for VSP < 0, which simplifies the computational procedure, will not increase the error in the estimation of CO₂ emissions.