Xumei Chen

Assessing Effect of Traffic Signal Control Strategies on Vehicle Emissions

Abstract In response to the increased traffic congestion and worsened air pollution, using the portable emission measurement system (PEMS), this paper collects and compares the real world emissions under signal coordination and non-coordination in Beijing, and analyzes the emission levels and distribution characteristics under these two control strategies. Furthermore, by integrating the microscopic traffic simulation model of VISSIM and the VSP-based approach of emission modeling, the paper develops an integrated microscopic simulation platform of traffic emissions, which is finally used to evaluate the impact of two traffic control strategies, alternative signal timing and traffic flow on emissions.

Estimation of Travel Time Values for Urban Public Transport Passengers Based on SP Survey

Abstract Quantitative study on the travel costs of urban transit passengers has great significance for scientifically evaluating social benefits of public transportation system. Analysis of travel time values is one of the most important parts of travelers travel cost estimation. According to the stated preference (SP) survey data for Beijing residents, factors that influence public transport values of travel time are analyzed and a Logit-based model is used. An improved SP survey based model is proposed, in which travelers income is introduced as a variable. The parameters estimating the travel time values under the trip purposes of work/business and leisure are calibrated. Then the values of travel time under different conditions in Beijing are obtained (i.e. different trip purposes and with/without transferring). The results indicate that the travel time values for work are generally higher than those for leisure. The waiting time values are higher than transferring time values and in-vehicle time values under any circumstances, and the waiting time values are higher with transferring than those without transferring.

Calibration of Vissim for Bus Rapid Transit Systems in Beijing Using GPS Data

Bus Rapid Transit (BRT) systems have grown in popularity in recent years. With the rapid development of computer technologies, using microscopic simulation models to study various strategies on planning, implementation and operation of BRT systems has become a hot research area in the field of public transportation. To make the simulation models accurately replicate field traffic conditions, model calibration is crucial. This paper presents an approach for calibrating the microscopic traffic simulation model VISSIM using Global Positioning System (GPS) data for application to Beijing BRT systems. The Sum of Squared Error (SSE) of the collected versus simulated vehicle speeds at the cross-sections along the test route is specified as the evaluation index. A Genetic Algorithm is adopted as the optimization tool to minimize the SSE. Taking the Beijing North-South Central Axis BRT Corridor as a case study, it shows that the proposed approach is a practical and effective method for the model calibration.

Development of City-Specific Driving Cycles for Transit Buses Based on VSP Distributions: Case of Beijing

With the rapid increase of automobile ownership, the city of Beijing, China, faces challenging issues with regard to traffic congestion and vehicle emissions. In seeking solutions to these issues, developing and improving public transportation systems is considered one of the most feasible and promising strategies because these systems have high passenger-carrying capacity and low pollution on a per passenger basis. Driving cycles reflect traffic conditions, and thus vehicle emissions, and form a scientific base to further improve bus operations. This paper is intended to develop city-specific driving cycles for transit buses for Beijing. The operational data of 126 buses were collected by using a portable global positioning system (GPS) for three types of bus routes: the bus rapid transit (BRT) line, express line, and regular line. Through analysis of the operating characteristics, a methodology for developing driving cycles is proposed based on the parameter of vehicle-specific power (VSP) distribution. Then, by applying this methodology, driving cycles for BRT, express, and regular lines are developed accordingly. Finally, the developed driving cycles are evaluated. Based on the analysis, the proposed driving cycles are able to reflect the real-world operating characteristics of transit buses better than other driving cycles. Furthermore, the emission factors generated based on the developed driving cycles are lower on average than those predicted by using the default driving cycles in the motor vehicle emission simulator (MOVES).

Microscopic Traffic Simulation Approach to the Capacity Impact Analysis of Weaving Sections for the Exclusive Bus Lanes on an Urban Expressway

This paper presents a microscopic traffic simulation approach to the capacity impact analysis of weaving sections caused by the installation of exclusive bus lanes (XBLs) on urban expressways. Three typical configurations of XBL in Beijing are identified, including median bus lane with off-on-ramp, curbside bus lane with on-off-ramp, and curbside bus lane with off-on-ramp. Then, the weaving section length, headway, mainline volume, as well as off-ramp and on-ramp volumes for general traffic are considered as parameters in designing simulation scenarios. Finally, the microscopic simulation is executed, by which the capacity of general traffic for weaving sections is estimated and the impact of the weaving section length and headway on the capacity is evaluated. It is found that the weaving section length and headway have different impacts on the capacity of general traffic in different configurations. The results also provide that the weaving section length and headway are more sensitive in the on-off-ramp than in the off-on-ramp scenario with the curb bus lane.

BRT Vehicle Travel Time Prediction Based on SVM and Kalman Filter

An integrated BRT vehicle travel-time prediction model was proposed that used the support vector machine (SVM) to predict the initial travel time and applied the Kalman filter algorithm to dynamically adjust the results of the predicted travel time. Based on the GPS data, a case study of the BRT line 2 in Chaoyang district, Beijing, was conducted with the help of the proposed prediction model. BRT vehicle travel time during the morning peak hour and the off-peak hour was predicted by both the proposed model and the Kalman filter model. The results prove that the proposed model is more suitable for predicting the BRT vehicle travel time with a high prediction accuracy, and the accuracy for the off-peak hour is higher than the one for the peak hours.

Microscopic Simulation Approach to Effectiveness Analysis of Transit Signal Priority for Bus Rapid Transit: A Case Study in Beijing

Transit signal priority (TSP) is one of the critical components of bus rapid transit (BRT) and a key technology in enhancing its operational efficacy. It not only provides priority to the BRT vehicle but also manages the trade-off between the delay of buses at an intersection and the impacts on other traffic. This paper focuses on the design and evaluation of a simulation of signal priority for BRT under mixed traffic flow conditions. Taking the Southern Axis BRT Line 1 in Beijing as a case study, different signal priority strategies, including green extension, red truncation, and special phase insertion, are developed for the signalized intersection along the BRT route. A signal coordination plan is designed for the section composed of four intersections in the BRT system. The study uses the VISSIM microscopic traffic simulation model to analyze the impacts of traffic parameters, especially those of nonmotorized traffic, on the effectiveness of TSP along the corridor. Simulation results indicated that the BRT vehicles would typically benefit from transit priority with travel times savings and delay reduction, as well as greater schedule adherence, and suggest that these benefits may be obtained with little negative impacts to the overall system. The results also indicated that the volume of nonmotorized traffic is one of the most important factors that influence the effectiveness of TSP implementation in a mixed traffic flow.

Support Vector Machine-Based Approach to Data-Layer Multi-Source ITS Data Fusion

Abstract Through a characteristic analysis of multi-source Intelligent Transportation System (ITS) data fusion on data layer combined with the concept of support vector machine (SVM), this article proposes a multi-source ITS data fusion technique using SVM, and designs a corresponding implementation approach from perspectives of SVM training, training result evaluation and SVM test. A comparison of data outputs derived from the SVM-based fusion and the real data before the SVM-based fusion, when the proposed technique is applied to a set of two-source traffic flow data from ShangJie on-ramp of BanShen highway in Japan, demonstrates that the proposed SVM-based fusion approach can implement the data quality control effectively, which improves the level of the data accuracy.

Double-Sided Optimization of ITS Data Aggregation Via Wavelet Transformation

Abstract This paper addresses a modeling approach to analyzing an integrated system that includes freeway mainlines, ramp metering, and an upstream signalized diamond interchange. The modeling approach takes into consideration of the various components, their operational characteristics, and their interactions within the system. Strategies are also proposed for real-time operation and possible field implementation. The key element of achieving an integrated operation is to control the ramp feeding the traffic through special signal timings at the diamond interchange. Whenever a long queue is detected at the metered ramp, the signal timing should be adjusted to reduce the traffic flows entering the ramp. In this way, the ramp meter will remain in operation as long as possible, which would delay the onset of queue flush (i.e., termination of ramp meter) and minimize the possibilities of a freeway breakdown. Because a diamond interchange is usually controlled by special signal phasing and timing, the control strategies are specially focused on the special diamond signal phasing schemes. The system design and system architecture are also presented for potential deployment of the system in the field.

Evaluation Analysis on an Integrated Fare Initiative in Beijing

An effective fare policy and structure will realize a reasonable combination of both public welfare and operational profit.This article presents an evaluation framework for an integrated fare initiative in Beijing. It explains a new set of 10 evaluations indices, which include public acceptance, social equity, convenience, change of subsidy, possibility of modal integration, feasibility of implementation, change of revenue, change of readership, improvement of operation control, and change of cost. The article examines a survey of Beijing Public Transit System users to assess three integrated fare strategies introduced by the agency. The results of the survey are subsequently used as the input data to the proposed evaluation framework.