Signal Priority Strategies And Modeling For Trams With Exclusive Lane

Urbanization and motorization brought traffic problems to city. Resource conservation and environmental protection become key issues in transportation development. Trams are planning and constructing throughout the world, because of its energy saving, comfortable, nice design and flexible types. Compared with foreign countries, technologies and projects in China are quite inadequate. Therefore, academic systems, professional standards, technical manuals and management requirements need to be built in a hurry. Moreover, trams integrate two operation environments including rail transit and road transit, which bring its characteristics of efficient transportation and influencing by general vehicles. It is necessary to study trams especially on the strategies and methods for its priority operating, so as to giving full play to its medium capacity, ensuring its operation efficiency and enhancing its service level and operational reliability.This paper summarizes and analyzes existing researches. It takes trams priority as object and developes signal strategies and modeling methods from two aspects including active priority and passive priority. In active priority, the influence of detector location on waiting time of trams at intersection, and threshold values of active priority are studied. In passive priority, arterial signal coordination model is optimized and new models are built for trams. Main researches and conclusions of this dissertation are summarized as follows.(1) Waiting time of trams at intersection is affected by detector location. Aiming at trams with active priority at isolate intersection including red truncation and green extension, this paper designes three scenarios according to the extra green time of trams phase from its former and later phases or the left non-priority phases, and if there is red truncation once trams stopped. After that, a calculation model is proposed by considering phase states, detector location and trams progressing speed, with waiting time of trams at intersection as objective function. Results using the model are tested by VISSIM. Moreover, the relationship between waiting time and detector location is studied further by setting various of trams speed and cycle time. The delays in three scenarios are also discussed at last.(2) There are reasonable ranges of priority time in red truncation and green extension. Threshold values of priority are modeled by taking vehicle delay and saturability as constraint conditions, priority time as independent variable, maximizing overall efficiency of the intersection as objective function. The model takes traveler instead of vehicle as delay object and uses Webster graphic method to solve delay according to the previous studies by other researches. In addition, the effect of trams’ long length on lower limit value of threshold is considered particularly. Threshold values of priority for trams are achieved through a case study which also proves that it is more reasonable by taking traveler as delay object for intersections with a lot of buses. The influences of arrival rate, buses number and red time of non-priority phases, and interval of trams on the threshold values are analyzed as well.(3) The arterial signal coordination optimization model for trams is proposed based on AM-BAND model. Two aspects of improvements are conducted.Firstly, it is found that there is unavailable bandwidth when left band broadens or right band narrows along the outbound direction, and left band narrows or right band broadens along the inbound direction. Thus, the conception of active bandwidth area is developed for BAM-BAND model who has extra active bandwidth constraints beyond AM-BAND. The comparison show that active bandwidth area increases 5% from BAM-BAND than AM-BAND, and travel time of trams outbound and inbound save 9% and 14% respectively.Secondly, several constrains regarding tram operations are incorporated to the BAM-BAND model including dwell time at stations, active signal priority and minimum bandwidth value, and BAM-TRAMBAND model is presented. The active priority in this model refers to detector location and threshold values studied former. The case study and VISSIM simulation show that travel times of tram in two directions decrease 12% and 20% respectively with signal plan from BAM-TRAMBAND comparing with the original signal plan. Traffic performance indicators such as stops and delay are improved significantly. Moreover, average bandwidth of segment from model with active priority constrains appears larger by 8s than model without active priority constrains, which means active priority make sense to improve bandwidth.(4) On the basis of BAM-TRAMBAND model proposed former, two arterial signal coordination optimization models for trams with train diagram constrains are developed, hard train diagram constrains model (HT-TRAM) and soft diagram constrains model (ST-TRAM). Supplementing constrains are departure interval, stopping time, running time in the sections, and travel time along arterial. In HT-TRAM model, trams progress according to train diagram strictly, while in ST-TRAM model, stopping time and running time of trams fluctuate in a small range. In the case study, weighted sum of bandwidth is higher for HT-TRAM than ST-TRAM by 10s, and average bandwidth of section is higher by 1s. Moreover, a numbering method is invented using station index and its location for realizing running time constrains.