# Real-Time Performance Measurement Application via Bluetooth Signals for Signalized Intersections
## 2 Materials and Methods
### General Principles of Real-Time Performance Measurement Application via Bluetooth Signals  
The method designed in this study can be applied to all signalized intersections. Signalized intersections are divided into types such as three-way intersections, four-way intersections, and rotary intersections. The number of lanes belonging to the arms may differ in each intersection. The method is designed to be applied to all signalized intersection geometric types. The designed system detects the travel times per vehicle with Bluetooth sensors placed at appropriate distances from the intersection arms and is associated with the real number of vehicles by fusion with the second sensor to be used at the intersection. Sensors that can count vehicles such as loop sensors, image-processing-based sensors, and radar sensors can be used as secondary sensors. Figure 5 shows an example application that can be carried out on a three-way intersection where the number of lanes belonging to directions are different. It is sufficient to use one of the loop sensors, image-processing-based sensors, or radar sensors as the second sensor. As seen in the example application, Bluetooth sensors are placed back from the intersection directions. Thus, the travel times of vehicles between the intersection arms are  
Figure 5: Application on sample intersection. determined. Delays per vehicle can be calculated based on the detected travel times and the total delay between the arms can be determined by multiplying them with the actual vehicle numbers coming from the second sensor. Thus, the intersection performance is measured in real time. For Bluetooth sensors, some considerations should be made in positioning to obtain more secure data, optimize range, and reduce interference. Bluetooth sensors are best placed at the end of the intersection where maximum queuing occurs from the stop line. Therefore, it is recommended that sensors be placed approximately 100 m behind the intersection stop line. Bluetooth sensors should be installed on roadsides. The location of the Bluetooth sensor should be near vehicle routes. The sensor can be mounted on existing poles or new poles can be erected if necessary. Bluetooth sensors can communicate well with devices in a suitable area radius within a 360-degree angle. Therefore, when choosing a location for Bluetooth sensors, the radius criterion, which is the area of effect, should be taken into account. Bluetooth signals use radio waves and can be affected by obstacles. Buildings, walls, trees, and large metal structures can block or reflect the spread of the signal. Sensors should be placed in places where there are no such obstacles and where there is a clear line of sight. The height of the sensors from the ground affects the signal coverage area and reception quality. It is recommended that the height at which Bluetooth sensors will be positioned is at least 3 m and at most 6 m. Sensors placed at a too-low height may cause signal loss or incorrect data due to reflections. The distance between the sensors should be adjusted to optimize coverage areas. Placing sensors too close to each other can lead to data redundancy and incorrect calculations. Sources of electromagnetic interference such as Wi-Fi routers and other Bluetooth devices should be avoided. These devices can interfere with Bluetooth signals. In order for sensors to work continuously, there must be a reliable power source nearby. For easy maintenance of sensors, they should be placed in easily accessible locations. This is important for periodic maintenance and troubleshooting. In the designed method, a technology called Adaptive Frequency Hopping Spread Spectrum (AFH) is used in the Bluetooth sensor to ensure data security. This technology allows Bluetooth devices to communicate without being affected by interference from other devices using the same frequency band. Constantly changing frequencies make it difficult for the signal to be monitored and for unauthorized persons to intercept the signal, which increases the security of communication.