Research And The Design On The Urban BRT Signal Priority Control Method At The Road Intersections

The city’s social and economic development has been affected seriously by traffic congestion, which should be studied and solved urgently. Hence developing the public transport becomes an inevitable choice and a top priority at domestic and abroad countries to ease the urban traffic problems. As the modified conventional transport means, Bus Rapid Transit(BRT) has many apparent advantages, including being economical and very convenient, being operated as block-train as well as larger carrying capacity. All of these can ease the traffic jam in a shorter time and help solve the problem of the increasingly sharpening contradiction between supply and demand. From the long-term perspective, BRT can adapt to and guide passenger demand better, and can expand the development of the city developing space, which makes it one of the effective ways to improve the urban traffic status.Based on the above analysis, aiming at designing BRT signal priority control system complying with China’s current conditions, both the BRT vehicle signal priority control methodology system and its strategies and optimization models are researched in this paper.Firstly, the concept of the conventional bus priority and the necessity of its development are analyzed, which then bring out the concept of conventional bus signal control priority strategy. Meanwhile the elaborated passive priority policy, the active priority policy and the real-time priority policy, as well as their respective control principles and the corresponding control flows are introduced. Moreover, the adaptability and the scope for the three control strategies are defined accordingly. As a result, these above contents lay a solid theoretical foundation for further study of the BRT intersection signal priority control.Secondly, in order to ensure the overall effectiveness of the intersections and the BRT priority at intersections, the optimization step control method adjusting to the combination of online and offline controls is designed and the optimized fix-time model is established. Since BRT passenger vehicles carry a larger proportion passengers at the whole intersection, it is natural to reduce the average delay for the vehicles whereas to reduce per capita delay. In order to ensure the priority of BRT passing the intersection and to avoid other vehicles longer delay, bi-level optimized time assignment model is worked out based on HCM2000 delay formula, whose goals are focused on the minimum waiting time for BRT and for per people at the intersection.Thirdly, in the process of the online optimization, the priority adjustment trigger conditions(PATC) are defined remarkably, such as PATC for the vehicles and PATC for the overall effectiveness. Combining the inherent information of the BRT vehicles with the dynamic tracking information, the urgency degree of BRT is calculated so that PATC can be judged. Furthermore, taking it as the goal to minimize the delay of all vehicles per capita afterthe BRT priority, the overall efficiency of the intersection can be improved by each BRT priority. Providing PI as performance indicators function, then the efficiency difference between the benefits of the priority and the deficiencies of the non-priority can be got,through which the priority trigger condition can be obtained.Finally, by making use of the micro-simulation software(VISSIM) to simulate a typical cross intersection offline control and online optimization of the operating states, the comparative analysis of the simulation results could verify the effectiveness of the sub-step control methods.