# Monitoring Technologies for Truck Drivers: A Systematic Review of Safety and Driving Behavior
## 3 Results
### Monitored Variables  
Identifying the variables monitored by truck driver monitoring technologies is essential for evaluating their effectiveness in improving road safety and driver performance. These technologies leverage specific physiological, behavioral, and environmental metrics, each offering unique insights into safety outcomes and operational efficiency. This section analyzes how the six primary monitoring technologies--wearable devices, in-vehicle monitoring systems, vision-based systems, ADASs, data logging and event recording systems, and connectivity and communication systems--contribute to a comprehensive framework for addressing the complex challenges of modern transportation systems. Wearable monitoring devices specialize in capturing physiological variables such as heart rate, heart rate variability, skin temperature, electrodermal activity, and blink rates. These real-time metrics provide critical insights into fatigue, stress, and alertness levels, which are particularly vital for long-haul operations. Additionally, wearable devices monitor behavioral variables, including posture, micro-movements, and physical activity patterns, to assess driver alertness and well-being. Complementing this, these devices track environmental variables, such as ambient temperature and humidity, which directly influence comfort and fatigue. Continuous monitoring across both daytime and nighttime contexts ensures a comprehensive understanding of the driver's physiological state under varying conditions. In-vehicle monitoring systems are designed to track behavioral variables such as hard braking, speeding, swerving, and unbelted driving, which are critical indicators of unsafe driving practices. These systems also monitor environmental variables, including road conditions, traffic density, and operational factors like load type and trip length. By enabling continuous monitoring over extended periods, often several months, these systems provide fleet managers with actionable data to identify driving trends and high-risk behaviors, facilitating targeted safety interventions and operational improvements. Vision-based monitoring systems are highly effective in capturing physiological variables such as blink rate, eye movement, and facial expressions, which are key indicators of fatigue and distraction. Additionally, these systems monitor behavioral variables like lane position, steering smoothness, and gaze patterns, reflecting driver attention and precision. Vision-based systems also track environmental variables, such as traffic density, road conditions, and visibility, offering real-time and contextualized insights into driver behavior across diverse scenarios, including both daytime and nighttime operations. ADASs primarily monitor behavioral variables, including reaction time, braking distance, deceleration patterns, and headway distance, to evaluate driver responsiveness and safety. These systems also capture environmental variables such as vehicle speed, proximity to other vehicles, and collision risks. By operating continuously in real-world conditions, ADASs enhance situational awareness and enable proactive safety interventions. Through the integration of driver behavior data with external environmental information, ADAS technologies play a pivotal role in accident prevention and the overall improvement of road safety. Data logging and event recording systems focus on capturing detailed behavioral variables such as speeding, harsh braking, and acceleration patterns, which are essential for identifying unsafe practices. These systems also monitor environmental variables like road conditions, weather, and operational settings. Continuous data logging facilitatescomprehensive post-trip evaluations and long-term trend analyses, making these systems indispensable for fleet management, regulatory compliance, and identifying areas for safety enhancement.