# Simulation Study on an ICT-Based Maritime Management and Safety Framework for Movable Bridges
## 4 Principle of the Study  
Two separate counting algorithms are implemented in parallel of which one ensures bridge evacuation and another confirms whether the ship has passed through the bridge. When bridge traffic enters the bridge through the entry lane, each traffic is detected with an object number. The number of vehicles entering through the bridge is counted by entry cameras \(Ca\) and \(Cc\) at both sides of the bridge. When one vehicle enters the entry lanes, it gives a value of one which is subsequently added to the aggregation of the total vehicle entered. When this vehicle passes the bridge through any of the exit lanes, the previously added value is subtracted from the total aggregation. The passing vehicles through exit lanes are detected through exit cameras \(Cb\) and \(Cd\). Thus, for the continuous transport of vehicles on the bridge, there is a continuous cycle of counting by adding value per vehicle's entrance and subtracting value from the total aggregation per vehicle's exits. In this paper, the case considered is continuous traffic flow through a movable bridge. The notation for this case is described below. Number of vehicles detected through the camera, \(Ca\) for different entry lanes = \(k\)  
Number of vehicles detected through the camera, \(Cb\) for different exit lanes = \(l\)  
Number of vehicles detected through the camera, \(Cc\) for different entry lanes = \(m\)  
Number of vehicles detected through the camera, \(Cd\) for different exit lanes = \(n\)  
Number of vehicles remaining between \(Ca\) and \(Cb\) = \(k-l\)  
Number of vehicles remaining between \(Cc\) and \(Cd\) = \(m-n\)  
Therefore, the total number of vehicles remaining in the movable part of the bridge = \((k-l)+(m-n)\)  
When the ship is identified by the prime buoy, the bridge control system automatically activates the road barrier of entry lanes. This prohibits further vehicle entrance to the bridge. When vehicles get through the exit lanes of both sides of the bridge, this total aggregation keeps reducing, and this turns to zero at the point when all the vehicles leave the bridge through exit lanes. This zero-count condition is considered an evacuated bridge. For the bridge traffic evacuated condition:  
Number of vehicles remaining between \(Ca\) and \(Cb\) = \(k-l\) = 0  
Number of vehicles remaining between \(Cc\) and \(Cd\) = \(m-n\) = 0  
The total number of vehicles remaining in the movable part of the bridge = \((k-l)+(m-n)\) = 0 For ease of understanding, the control system is divided into three domains: the ship control system, the bridge control system, and the vehicle control system. The systems are shown as large circles in a relation diagram in Figure 5. The figure provides an overview of the data flow and transmission of warning signals depending on the velocity and time of the ships, on-bridge vehicles, and the bridge movement. It is seen from the figure that when the ship crosses its first (incoming) alert belt, it sends its data through the buoy to the bridge control system to assess whether its specification calls for the bridge to open. If it does, the bridge sends the on-bridge vehicle control system to activate the traffic billard unit, start the counting algorithm, and calculate the time required for the bridge evacuation. If the ship reaches the Emergency Belt before bridge nullification, the bridge is commanded to be opened. However, if there is a chance of collision, the ship is given a distress signal to either control its speed to decrease until nullification. The bridge control system can also force stop the ship through the DSRC radio communication. A complete flowchart of the control system of movable bridge maritime management is illustrated in Figure 6.  
Figure 5: Relationship diagram for the three control systems in ships, vehicles, and bridge. Figure 6: Flowchart for the control system of movable bridge maritime management and collision prevention.