Authors: Yongjie Lin, Xianfeng Yang, Gang-Len Chang, and Nan Zou
Conference:  92th TRB Annual Meeting in 2013
Abstract: This paper presents a transit signal priority (TSP) model designed to consider the benefits of both bus riders and all intersection passenger car users. The proposed strategy, mainly for headway-based bus operations, offers the responsible agency a reliable way to determine the optimal green extension or red truncation duration in response to multiple bus priority requests from different routes. The control objective is to minimize bus passenger waiting time at the downstream bus stop while ensuring that the delays for all passengers are not increased. Using the field data from Jinan, China, the proposed strategy has shown its promise in reducing the bus passenger waiting time and the total intersection delay. Our further exploration with simulation experiments for sensitivity analysis has also found that TSP will be most effective if the ratio between bus and passenger volumes exceeds the threshold of 2 percent.

Download (Transit_Priority_Strategies_for_Multiple_Routes_under_Headway_based_Operations.pdf)

Authors: Seonyeong Cheong, Saed Rahwanji, and Gang-Len Chang
Conference: The 11th International IEEE Conference on Intelligent Transportation System, October 2008 in Beijing, China
Status: Presented
Abstract: This research is aimed to evaluate and compare the operational performance of three unconventional intersections: Continuous Flow Intersection (CFI), Parallel Flow Intersection (PFI) and Upstream Signalized Crossover (USC). For this purpose, various experimental designs, including traffic conditions, geometric features and signal plans, were set and the average delays were compared for movements of through-only traffic and left-turn-only traffic. From the results of analysis, all three unconventional intersections outperformed conventional one and among the unconventional intersections, CFI outperformed the others except for some traffic conditions. In the balanced traffic condition scenario, at the low traffic volume level, the average delays of through traffic for PFI were smaller than that of CFI and very similar at the moderate traffic volume level. And this research showed one possibility that the average delays of left-turn-only traffic at PFI will be closer to that of CFI as the traffic volume increases. In the unbalanced traffic condition scenario, under some traffic conditions, PFI outperformed CFI or showed very similar average delay with CFI. And generally, there were not much difference in the average delays between CFI and PFI as compared with that between CFI and USC under the experimental traffic conditions of this research. Considering the accessibility and land use problems of CFI, PFI is a good alternative to reduce the average delays, which is comparable to CFI, and as well reduce the property impact and cost.

Download (Seonyeong_IEEE08_1.pdf)

Authors: Xianfeng Yang, Yao Cheng, Gang-Len Chang
Conference: ITS world congress, 2014
Abstract:  Congestion at the downstream of a freeway off-ramp often propagates the traffic queue to the mainline, and thus reduces the freeway capacity at the interchange area. Hence, an accurate queue estimation model can help the traffic engineers to select proper control strategy to mitigate queue spillback at off-ramps. In responds to such a need, this study presents a queue estimation system using dual-zone detectors, where each detector can provide two detection zones. Particularly, the short detection zones are used to count traffic flow rates and the information from long detection zone can indicate the presence of traffic queues. With respect to different congestion levels, the off-ramp queue may be fully discharged during the green time or not. Therefore, this study has developed two queue estimation models for each condition. Based on the field data from the freeway interchange in Zhubei, Taiwan, this study has conducted extensive simulation experiments, and demonstrated the effectiveness of the proposed system on off-ramp queue estimations.

Download (Real-Time-Traffic-Queue-Length-Estimation-at-Freeway-Off-ramps.pdf)

Authors: Xianfeng Yang, Yang (Carl) Lu, Gang-Len Chang
Conference: 2013 Transportation Research Board 92nd Annual Meeting
Abstract: This study presents two models for proactive VSL control on recurrently congested freeway segments. The proposed basic model uses embedded traffic flow relations to predict the evolution of congestion pattern over the projected time horizon, and computes the optimal speed limit. To contend with the difficulty in capturing driver responses to VSL control, this study also proposes an advanced model that further adopts Kalman Filter to enhance the accuracy of traffic state prediction. Both models have been investigated with different traffic conditions and different control objectives. Our extensive simulation analysis with a VISSIM simulator, calibrated with field data from our previous VSL demonstration site, has revealed the benefits of the proposed VSL control model, compared with the case without VSL. Also the results indicated that both proposed proactive models can outperform the basic models and significantly reduce the travel time as well as number of stops over the recurrent bottleneck locations. With respect to several selected MOEs, such as average number of stops and average travel time, it has been found that the one with the control objective of minimizing speed variance clearly outperforms other models.

Download (Proactive_Optimal_Variable_Speed_Limit_Control_for_Recurrently_Congested_Freeway_Bottlenecks.pdf)

Authors: Yao Cheng, Xianfeng Yang, Gang-Len Chang
Conference: Transportation Research Board, 2015
Abstract: Conventional Transit Signal Priority (TSP) controls often reach a limitation for arterials accommodating heavy bus flows since the priority function can significantly increase  delay at minor streets. To improve reliability of bus operations and increase the bus ridership, a bus-based  progression model that considers the operational characteristics of transit  vehicles is developed. The VISSIM simulation with an arterial consisting of five intersections and three  two-way bus stops demonstrates that the  proposed model can significantly reduce  bus passenger delay and the per person