# Design and Testing of a Wearable System for Monitoring Car Drivers
## 2 Materials and Methods
### Testing Layout and Modes  
The testing layout was designed to simulate real-world driving conditions and to capture data related to aggressive driving behaviors. The setup included strategic placement of sensors on the driver's body and the use of different test modes to simulate various driving scenarios. Figure 3: Conceptual design of the proposed solution with three wearable units hosting sensors and other equipment communicating data via Bluetooth. The sensors were placed to capture relevant physiological and movement data effectively in the following locations:  
* Wristband: it is installed on the wrist to monitor heart rate, skin conductance, and the wrist movement for sudden steering wheel maneuvers. * Torso Box: it is attached to the torso to capture upper body movements. * Headband: it is worn on the head to measure head movements. In particular, the IMU data from the torso box and the headband will also provide information on neck acceleration, indicating aggressive driving due to large movements of the torso and head. The location of the sensor units is indicated in Figure 4 with a solution ensuring a wearing solution without excessive discomfort for a car driver. The system was tested in various modes to ensure data collection for the following conditions:  
* Normal Driving: Tests were carried out under standard driving conditions to establish a reference for physiological and movement parameters using all the device sensors. * Aggressive Driving: A driver performed aggressive maneuvers such as rapid accelerations, hard braking, and sharp turns. This mode aimed to capture the physiological and movement responses associated with aggressive driving. To proceed with the various test modes, the following experimental procedure was implemented:  
* Baseline Measurement: Initial measurements were taken during a period of calm driving to establish baseline physiological and movement data. * Simulated Driving Modes: A driver was instructed to perform aggressive driving maneuvers while the system recorded heart rate, GSR, and IMU data. * Data Analysis: The collected data were analyzed to determine if any parameter exceeded its threshold for calm driving by using a criterion value for the driver's level of aggressiveness. Figure 4: Location of the sensor units on a car driver: wristband with monitor heart rate sensor, skin conductance sensor, and IMU sensor; torso box with IMU sensor; and headband with IMU sensor. A criterion for the driver's level of aggressiveness can be proposed to quantify driving aggressiveness using the parameters acquired by the sensors of the proposed monitoring device as follows:  
\[ADC=W_{n}\;a_{n}+W_{w}\;a_{w}+W_{h}\;r_{h}+W_{s}\;c_{s} \tag{1}\]  
where \(W_{n}\) is the weighing coefficient for the value of the neck acceleration \(a_{n}\); \(W_{w}\) is the weighing coefficient for the value of the wrist acceleration \(a_{w}\) ; \(W_{h}\) is the weighing coefficient for the value of the heart rate \(r_{h}\); and \(W_{s}\) is the weighing coefficient for the value of the skin conductance \(c_{s}\). Table 1 summarizes the components of the proposed aggressive driving criterion (ADC), including each parameter's threshold value, weighting coefficients \(W_{i}\), and the rationale for its weighting. As reported in Table 1, the index ADC combines motion data with heart rate and changes in skin conductance due to sweating. While, from a medical perspective, heart rate and sweating can be accurate markers of aggressive behavior, the quality of the relative sensor acquisitions is strongly influenced by sensor placement, since a wrong installation can result in non-usable data or false positives. Conversely, while wrist and neck motion could be caused by different behavior, the relative sensing systems, based on IMUs, are easy to install and reliable. Because of this, the aggressive driving criterion weighs IMU measurements more than heart rate and skin conductance.