What Are The Signalling Control Systems? What Are The Types? (Chapter 3)
Pedestrian Warning System
Signaling systems are generally installed at intersections, entry and exit of connection roads and pedestrian crossings without intersection. Pedestrian crossing which are far from the intersections, continuously or at certain times of the day, signalling system which are definite time can be applicable to allow pedestrians to pass safely. Where there is a low pedestrian flow, the continuously right of way to vehicles is interrupted by pedestrians pressing the pedestrian buttons.
Control System of Adabtive Signalling
Adaptive traffic signalling control systems emerged in the 80s and they are widely used systems especially after 2000s. Adaptive control systems are one of the most advanced and complex control systems available today and continue to be developed.
Adaptive systems capture real-time data from sensors, instead of macthing current traffic conditions with current signal time plans, it dynamically generates the best signal time plan instantly. In this case, there is no need library for signal planning, system is preferred when demand is high and time schedules need to be changed frequently. The distinctive feature of the software used in adaptive systems is that they contain algorithms based on optimization.
Fixed-time control system cannot response the traffic demand which is changing depand on the time, the signal duration is sometimes too long and sometimes insufficient. Therefore, dynamic (variable according to traffic) control systems are preferred especially for responding to variable traffic conditions. Adaptive control systems are the most adaptable to the change of traffic in dynamic systems.
Besides, when a sensor fault occurs in some systems, calculations are performed using historical count data. In some systems, the data obtained from the sensors placed at the intersection’s exits and the instant traffic situation are recorded in the system and the arrival of vehicles is estimated from the periodic flow profile. Thus, the green time is created according to the queue to which vehicles arriving at the intersection point during the red duration.
Adaptive traffic signaling control systems, especially when the traffic is dynamic (variable) and in case where this variability varies considerably over time it can achieve very successful and satisfactory results compared to other systems. However, traffic flows; it can vary according to many factors such as traffic conditions, driver behavior and geometric characteristics. No general conclusions should be reached such as adaptive system implementation at all times and in all circumstances, all conditions should be examined carefully and a decision should be made by especially considering the installation and maintenance costs of the sensors.