Delay Correction Model For Estimating Bus Emissions At Intersections

Buses have the advantages of large capacity, high efficiency, and low emissions per person. Thus, the development of the bus transit system can not only mitigate the urban traffic congestion, but also reduce vehicle emissions and energy consumptions. It is known thatvehicle emissions at intersections are higher than on the road sections, which are also densely populated points. Though at present, there have been some studies on estimating bus emissions at intersections.Few researchers have developed the quantitative model relating the commonly used operational performance indexes with bus emissions at an intersection. In this context, the research in this thesis intends to analyze the relationship between commonly used operational performance indexes and emissions of buses at an intersection.Based on large amounts of emission data and activity data, which are obtained from diesel buses in Beijing, the relationship between the delay and emissions is analyzed, followed by the establishment of the delay correction model for estimating diesel bus emissions at intersections based on VSP distribution. First, the VSP binning method is adopted and improved, in which an equal VSP interval of lkw/t is used. When both the speed and acceleration are zeros, the VSP Bin is defined as Bin16. The emission rate of the diesel bus for each VSP Bin is obtained from the massive emission data collected using the Portable Emission Measurement System (PEMS), from which the VSP-based emission estimation model for diesel buses is developed. Then, the study zone at an intersection is determined according to the types of intersections and turning movements of buses. In this study, a total of2,002sets of activity data collected by the Global Position System (GPS) are selected. The Delay and VSP distribution for each set of activity data are calculated. VSP distributionsfor different delays at different type intersections (Minor Arterial@Minor Arterial Intersection and the Minor Arterial@Collector) and different stops (no stop, one stop and two stops), are analyzed. It is found that the VSP distribution for no stop is similar to a normal distribution. The VSP fraction in Bin0is high, which decreases progressively from Bin0to two sides. And the VSP fraction in Bin16is zero. VSP distributions are similar between one stop and two sops. The VSP fraction in Bin16is much higher than other Bins, which increases with the increase of the delay, but its increasing ratedecreases gradually. For both types of intersection, VSP distributions are similar. The VSP fraction in Bin16is high. But when the delay is low, the VSP distribution at Minor Arterial@Minor Arterial Intersection is more centralized than that at the Minor Arterial@Collector Intersection around BinO. Further, the emission factor of each activity data is calculated, and the baseline emission factors for different types of intersections are determined. As a result, delay correction factors are calculated for two types of intersections and different stops in different delays. The analysis shows that the relationship between delays and delay correction factors is linear. Subsequently, the delay correction models for emission factor are developedfor two types of intersections and different stops.Finally, the significance test is conducted on the proposed model by using the SPSS software. Further, the validity test of delay correction models is conductedby using the real-world activity data. The test results demonstrate that the delay correction model is able to estimate the diesel bus emissions accurately at the intersection.