## Materials and Methods
### Vehicle Detection and Sensors at Intersections  
Sensors are extremely important components for smart transportation systems. Their use enables the development of a wide variety of applications for traffic safety, traffic control, and driver assistance. The use of analytical methods in traffic flow problems was initiated with the use of sensors integrated with transportation systems. This integration has also paved the way for a wide variety of next-generation smart applications that aim to improve the security and traffic control of existing and future transportation systems.  
It is extremely important to support the system management with the data flowing from the field to perform the system control in signalized intersections. By placing detectors or sensors inside the intersections or connecting roads, it becomes possible to control and plan the signal according to the number of vehicles and density ratios, or to pedestrian or bicycle activity. The traffic signal controller can then use this information to perform functions, such as allocating the amount of green time, selecting timing plans, and determining the sequence of transitions between phases.  
Different sensors can be used in signalized intersections depending on factors such as intersection geometry, location, and capacity. Sensors are classified into two main groups according to their positioning: on-road/under asphalt (intrusive) or roadside at ground level (non-intrusive) [40]. Sensors such as cameras, radar, laser, infrared or ultrasonic are used roadside, while other types of sensors are used on the road/under asphalt, such as pneumatic road tubes, magnetic loops (loop detectors), and piezoelectricity. Intrusive sensors are placed under the asphalt or at road level [41]. They have high sensitivity and can be applied in a wide area, but at the same time, the installation effort, maintenance, and repair costs are quite high. Additionally, they are more affected by weather conditions (i.e., snow, rain, fog). Figure 4 shows the explained different types of these sensors.  
Non-intrusive sensors are installed in different places as shown in Figure 5. These can see the road remotely and can detect parameters such as vehicle passage, speed, type, and lane capacity. These systems are more costly and more affected by environmental conditions compared to sensors located on asphalt. Remote, on-road sensors are mainly used to develop applications that provide information, such as queue detection at a traffic light, traffic conditions, road weather conditions, highway capacity, and current density.  
Figure 4: Intrusive sensors placed on or under asphalt [40].  
Some sensors are mounted on a pole and used to monitor a specific coverage area, while others are mounted directly at bridge crossings above the road area to be monitored [40].  
Acquiring the correct data flow is extremely critical in evaluating traffic conditions. This requires the use of the correct sensors in the correct locations and conditions. Positioning the sensors is done at the beginning with the intersection plans. Figure 6 shows the intersection plan made before the installation of the sensors. It has been noted that cameras and loop detectors are predominantly used at the intersections examined within the scope of this study. In this paper, there are indications that both systems have advantages and disadvantages in comparison. Moreover, different evaluation alternatives are formed according to the used technology. The resulting differences are mentioned in the discussion section of the study.