# Semantic Traffic Sensor Data:
## 3 Traffic Modelling in TRAFAIR
### Modeling of Data Provided by Traffic Sensors
#### 3.2.1 Traffic Sensors in Two Representative Cities  
For illustration, the traffic sensors used in two representative cities within the context of the TRAFAIR project (Modena and Zaragoza) are mentioned in this section.  
The traffic sensors used in Modena are induction loops that are insulated electrically-conducting loops installed under the road surface. A lead-in cable connects the loop to the detector, which is an electronic unit that detects the presence of vehicles above the loop. In these sensors, the vehicle passing over the sensor is registered by an increase in inductance. An induction loop can be located in a specific lane of a street to count the number of vehicles passing over it in a specific direction. In Modena there are 400 induction loops (see Figure 1). Three hundred forty-six induction loops are managed by the City Council (the blue markers in Figure 1) and are distributed around the city center, on almost every road of junctions with traffic lights. In contrast, 54 induction loops are placed on regional and municipal roads under the control of the Emilia Romagna Region (the magenta markers in Figure 1). Sensors provide, along with the identifier of the sensor, the number of vehicles passing over the sensor during a time interval, the timestamp of the beginning of the time interval, and the average speed.  
In the case of Zaragoza, the Zaragoza Council has Bluetooth antennas distributed around the city. Besides, several \"links\" have been defined as specific routes from one antenna to another antenna: the average speed of the vehicles that went through a link within a specific time interval (5 min) is computed by considering the distance between the antennas and the time needed by the vehicles to traverse that link. After that, according to that average speed, a color is assigned to each specific route to show the data on a map. Besides, the Zaragoza Traffic Control Center also provides us with some historical data obtained by both static devices and mobile devices measuring the traffic flow of different road segments in the city:  
Figure 1: Induction loops in Modena (the blue and magenta markers indicate the position of sensors managed by the City Council and the Emilia Romagna Region, respectively). Map data: Google, 2020.  
* Traffic static devices, which are 46 devices installed in different positions of the city of Zaragoza. More specifically, they are inductive coils located under the asphalt. These devices provide data about the traffic for 24 h a day for all the days in a year. Usually, there are two devices on the same road, one for each direction of circulation. However, in a few exceptions (specifically, for two cases), there is only one device measuring the traffic in just one direction. In Figure 2, a representation of the positions of these sensors is provided (shown with green markers).
* Traffic mobile devices, which are mobile traffic-detecting devices installed in 594 different points of the city throughout the year. Usually, there are also two devices on the same traffic road (one for each direction of circulation), as it is also the case for static devices. With these devices, data about the traffic measured during 24 h can be obtained (usually during only one or two days in a year, as these devices are located at fixed positions only for a few days).  
The traffic sensors, described in this section, are equipment belonging to the cities of Modena and Zaragoza. These sensors were already in place when the TRAFAIR project started (they were previously installed by the corresponding city councils), and the respective city councils collaborate with the TRAFAIR project by providing and facilitating access to those data.