Analyzing bus signal priority: a case study in Istanbul

Variety of policies have been implemented to solve increased private car usage problems. One of these policies is to increase the usage of public transportation. There are various applications that help to increase the usage of public transportation. One of the applications made in line with these policies is signal priority for public transport vehicles. The signal priority is not a new application, it has been used since 1970s. Buses are the predominant form of public transport in most towns and cities in many countries. In small / medium-sized towns and cities, buses are often the only form of public transport. With their large carrying capacity, buses make effective use of limited road space, and can therefore make a substantial contribution to reducing traffic congestion. Bus travel time is affected by many factors including traffic signals and traffic condition. Even though there is a big difference between the numbers of the passengers in the cars and in the buses, both of them are given equal priority at the traffic signals. The bus signal priority gives more green time or less red time at traffic signals to offers solution for the inequality. In spite of having negative effect on other vehicles, the bus signal priority produces a solution that is proportional to the number of passengers in vehicles and contributes to the increase of public transportation usage and helps to eliminate traffic congestion. The first advantage of the bus signal priority application is that it reduces the passengers times spend in the traffic by reducing the travel time of the buses. Secondly, it ensures compliance with bus travel times and increasing the reliability of buses, it is necessary to ensure that passengers know in advance the exact time they will finish their travel and increase passenger satisfaction. Finally, it provides economic benefits on the road network. Bus signal priority also has the potential for reducing overall delay at the intersection on a per person basis. At the same time, bus signal priority attempts to provide these benefits with a minimum of impact on other facility users, including cross-traffic and pedestrians. Bus priority at traffic signals has been implemented in large number of cities around the world. Bus signal priority can be implemented in a variety of ways. Priority treatments include passive priority, early green, green extension, phase insertion, phase rotation. Priority system components consist of three major elements, the transit vehicle detection / priority request system, the traffic signal control system, and a communications system to link the vehicle detection system with the traffic signal control system, possibly through a transit/traffic management center. It is important to note that although priority and preemption are often used synonymously, they are in fact different processes. While they may utilize similar equipment, signal priority modifies the normal signal operation process to better accommodate transit vehicles, while preemption interrupts the normal process for special events such as an approaching train or responding fire engine. Objectives of emergency vehicle preemption include reducing response time to emergencies,improving safety and stress levels of emergency vehicle personnel, and reducing accidents involving emergency vehicles at intersections. On the other hand, objectives of transit signal priority include improved schedule adherence, improved transit efficiency, contribution to enhanced transit information, and increased road network efficiency. Simulation softwares have become very important tools for evaluating the alternative traffic assignment and traffic control applications at urban transportation systems. Also they become useful tool in a variety of transportation problem settings. So simulation modelling is seen as an important aid to pre-implementation assessment. The simulation model is made by PTV VISSIM software because, among others advantages, it enables micro simulation of the area of interest by simple construction and editing of traffic network, modeling of vehicles with different characteristics, the psychophysical modeling of driver behavior (Wiedemann model), the stochastic definition of traffic parameters (speed, acceleration, power, dwell time, etc.), traffic signals modeling and effective outputting of results for further evaluation and interpretation. The sections of this study and the topics examined in these sections are briefly explained below. Chapter one contains objectives of the bus priority. Chapter two comprises the literature review. Chapter three comprises simulation and modelling. Chapter four of this thesis encompasses brief information about bus transportation in Istanbul. Chapter five contains the case study of thesis. The study site is a signalized intersection in Osmanbey İstanbul. The traffic volume counts is made at the signalized intersection and the intersection is modeled with the VISSIM simulation software. Then, the bus signal priority is applied by implementing the strategy of green extension, and the current situation and the bus priority situation, are compared. As a result modeling, it is found that the average delay per bus on the intersection is calculated as 27.5 s. in the current situation and it is 18.5 s. with 9.0 s. decreasing when the bus priority is applied. Despite this decrease on the bus delay, it is determined that the delays of cars at the intersection have increased. The average delay per car is 24.5 s. in the current situation and it is 28.4 s. when the bus priority is applied. The average delay per person in the current situation is 23.0 s., and it decreases by 0.8 s. to 22.2 s. when the bus priority is applied. The average delay per person decreases by 3.5% compared to the current situation.