Wanjing Ma

Investigating the Impacts of Green Signal Countdown Devices: Empirical Approach and Case Study in China

This paper presents an extensive investigation regarding the impacts of green signal countdown devices (GSCD) on the intersection safety and efficiency, based on field observation of critical driver and vehicle related parameters at two similar intersections (one with GSCD and the other without GSCD) in Shanghai. Statistical analysis results have revealed that the installation of GSCD can 1) encourage drivers to pass the stop-line during the yellow phase with higher speeds, and thus result in better utilization of the yellow phase and increased capacity of the intersection approach; 2) smooth the drivers response to the phase transition and effectively prevent the sudden change of speeds; 3) effectively eliminate the intersection dilemma zones by allowing the drivers to envision the phase transition and make decisions in advance; and 4) significantly reduce the number of red-light violations. Despite its effectiveness in facilitating the driver decision-making process, the installation of GSCD may adversely increase the possibility of collisions with unexpected crossing vehicles or pedestrians due to the significantly increased speeds of vehicles approaching the yellow phase. The analysis results from this study will offer the basis for traffic practitioners, researchers, and authorities in China to assess the impact of GSCD with respect to its operational and safety performance, and propose guidelines for its proper field installation.

A Dynamic Programming Approach for Optimal Signal Priority Control Upon Multiple High-Frequency Bus Requests

This article presents a priority signal control model for multiple bus requests. The proposed model aims to generate the optimal priority serving sequence to maximize the utilization of available green times by buses, but not to incur excessive congestion for other vehicular traffic. This study first depicts the serving sequence for multiple priority requests as a multistage decision process and explicitly models three bus priority strategies under the constraints of minimum green time, acceptable degree of saturation, and length of priority window. Further, it formulates a dynamic programming model to optimize the serving sequence for multiple priority requests as well as the corresponding signal timing plans under various levels of bus occupancy, schedule deviation, and traffic demand. A rolling time horizon approach is employed to solve the proposed model in real time. Comparative analysis results have shown that the proposed dynamic programming model outperforms the first-come-first-serve policy in terms of reducing bus delays, improving schedule adherence, and minimizing the impacts on other vehicular traffic. Computational performance analysis has further demonstrated the potential of the proposed model and algorithm to be applied in real-time bus priority control system.

Development and Evaluation of a Coordinated and Conditional Bus Priority Approach

One problem in existing bus priority strategies is that while a decision is being made to grant priority at an intersection, the bus arrival time at the downstream intersections is not considered. Moreover, only strategies for late buses are discussed; the strategies for early buses are seldom studied. This research tests a different bus priority approach, coordinated and conditional bus priority (CCBP). Coordinated, signalized intersection groups are adopted as control objects. Buses are detected one or more cycles before their arrival at the first intersection of the control object. A CCBP, with two kinds of priority strategies (increasing and decreasing bus delay strategies), is proposed. A model was built to generate the optimal combination of priority strategies for intersection groups so that the real delay of buses would be close to the permitted delay defined by the bus operation system. In the field application, the CCBP approach is compared with other two options: no priority and unconditional priority. Significant reductions on bus delay deviation and bus headway deviation were achieved with the use of the CCBP approach. Application of the CCBP approach resulted in only minor increases in total average delay of motor vehicles. The results of the field application studies performed as part of this study suggested that the CCBP approach could be used to decrease bus delay deviation and enhance the reliability of bus service without significantly affecting the delay of other motor vehicles.

Increasing the Capacity of Signalized Intersections with Dynamic Use of Exit Lanes for Left-Turn Traffic

Many congested intersections have a heavy traffic volume on movements for which capacity is insufficient because of geometric limitations. An unconventional approach that increases the capacity of heavily congested intersections is presented: this approach opens up exit lanes for left-turn traffic dynamically with the help of an additional traffic light installed at the median opening (the presignal); this situation is referred to as exit lanes for left-turn (EFL) control. An optimization problem for EFL control was formulated as a mixed-integer nonlinear program, in which the geometric layout, main signal timing, and presignal timing were integrated. The mixed-integer nonlinear program was solved by transformation into a series of mixed-integer linear programs. The latter problem can be solved with the standard branch-and-bound technique. The results of extensive numerical analysis and VISSIM simulation showed that the EFL approach could increase intersection capacity and reduce traffic delay substantially, especially under high left-turn demand. Moreover, the EFL control can be applied to one or multiple legs simultaneously; thus the control is particularly useful for intersections with an unbalanced left demand and a degree of saturation in travel directions.

Integrated design and operation of urban arterials with reversible lanes

Reversible lane operation, an effective strategy to relieve traffic congestion in urban arterials, must interact with other conventional traffic management and control components in the arterial, including left-turn restriction, lane channelisation, and signal timings. This paper develops a lane-based optimisation model to guide the integrated setting of reversible lanes and other traffic management measures in an arterial to maximise its operational performance. The optimisation problem is formulated as a multi-objective mix-integer non-linear programming model, which is then transformed into a single-objective mix-integer linear programming formulation for an optimal solution. Results from extensive numerical analyses have demonstrated the effectiveness of the proposed model.

Effective Coordinated Optimization Model for Transit Priority Control Under Arterial Progression

With the goal of providing effective priority control for transit while minimizing adverse impacts on general traffic movements along the arterial, this paper presents a coordinated transit priority control optimization model with the following features: (a) the control unit is defined as the coordinated intersection group between two successive bus stops; (b) buses are detected after leaving the upstream stop before their arrival at the first intersection of a control unit; (c) the dynamic interactions of priority strategies between adjacent intersections within a control unit are modeled by using a bus delay model and an ineffective priority time model; and (d) a linear program model is developed to generate the optimal priority strategies to reduce bus travel time when priority is necessary and to ensure that every priority treatment implemented at each intersection is effective. Extensive experimental analyses, including time–space diagram-based deterministic analysis and simulation-based analysis, were performed, and results were compared with conventional transit signal priority strategy and no-priority scenarios. The proposed model presents promising outcomes in the design of transit priority signal control in terms of decreasing bus delay, improving bus schedule adherence, and minimizing the negative impacts on general traffic under different traffic demand patterns.

Locating Urban Transit Hubs: Multicriteria Model and Case Study in China

This paper presents a comprehensive model for ranking candidate location plans of multiple urban transit hubs, which can effectively capture various aspects of concerns in the transit hub location planning process, including the overall efficiency of the transit network, the transfer intensity, the proximity to major passenger generators/attractors, the effectiveness of hub service coverage, the compatibility with land use restrictions, and the adaptability to future developable transit concepts. Grounded on an analytical hierarchy process (AHP)-based framework integrated with fuzzy logic, the proposed model offers the strengths to effectively determine the weights for multiple evaluation criteria and to synthesize the final score of each candidate plan for comparison. Results from a case study in Suzhou Industrial Park, China, reveal that the proposed model offers some promising properties for transportation planners to use in planning of transit hub locations. Comparative studies with respect to differe...

Implementation and Testing of Cooperative Bus Priority System in Connected Vehicle Environment: Case Study in Taicang City, China

Most previous work on the bus priority operation problem merely focused on dedicated bus lanes or transit signal priority. With the advancement of wireless communication technologies and the development of vehicle-to-vehicle and vehicle-to-infrastructure systems (i.e., connected vehicles), the opportunity has arisen to optimize traffic light, bus speed, and holding times at nearside bus stops simultaneously to provide priority for public buses. The study reported in this paper demonstrated the design and implementation of a cooperative bus priority system on the basis of connected vehicle technology. The system function, system architecture, and optimization strategies are presented. The system was deployed and validated at an intersection with two adjacent bus stops in Taicang City, Jiangsu Province, China. The results of the field test showed that the proposed system could reduce travel time and could decrease the number of stops. The successful demonstration showed that the potential was high for more efficient, integrated transit priority operation strategies on the basis of connected vehicles.

Multiobjective Optimization of Signal Timings for Two-Stage, Midblock Pedestrian Crosswalk

To improve convenience and safety for pedestrians, signalized two-stage, midblock pedestrian crosswalks are increasingly being installed in highly populated areas in developing countries such as China. This paper presents a multiobjective optimization model and its solution algorithm for optimal control of a two-stage, midblock crosswalk on a street with both vehicular and pedestrian traffic. The proposed model aims to produce the optimal signal timings at the crosswalk to accommodate both traffic modes and to adjust the offsets of the pedestrian signals for the two stages concurrently to minimize pedestrian delays and relieve congestion at a central refuge island, the safe area for pedestrians to stop. The proposed model and algorithm have three distinguishing features: (a) they explicitly model pedestrian delays at the two-stage controlled crosswalk, including delays at both the curbside and the central refuge island; (b) they model the number of pedestrians waiting on the central refuge island according to the change in signal timing; and (c) they have application in a multiobjective optimization approach to study the effectiveness of mid-block crosswalk control under conditions in which the priorities between vehicular and pedestrian traffic differ. A heuristic based on nondominated sorting genetic algorithm II was designed to solve the model and generate the Pareto solution set for signal timings. The results of the case study showed that the proposed model would help traffic practitioners, researchers, and authorities properly design signal timing plans and central refuge islands for two-stage midblock pedestrian crosswalks.

Cluster-Based Hierarchical Model for Urban Transit Hub Location Planning: Formulation, Solution, and Case Study

A cluster-based hierarchical location model for the selection of the proper locations and scales of urban transit hubs was developed with the objective of minimizing the demand-weighted total travel time. As an improvement to previous work, the proposed model has the following unique features: (a) it incorporates a hierarchical hub network topology that uses the concept of hub hierarchy establishment, route categorization, and service zone clustering to capture the critical operational issues for the transit network in an efficient manner and (b) it extends the previous nonhierarchical model to account for the impacts of hubs with various hierarchies as well as their interactions with lane use restrictions. An enhanced set of formulations along with the linearization approach was used to reduce significantly the number of variables and the computing time required to achieve the global optimum. The results of a case study in Suzhou Industrial Park in China revealed that the proposed model and solution method are quite promising for use in the planning of hub locations for the transit network. Sensitivity analysis of the performance of the system was also done to assist planners with the selection of the hierarchical structure and the design of transit routes.