## 2 Literature Review  
### Automated Safety Monitoring Systems for Real-Time Environments  
Studies report that construction workers may not recognize 33-57% of potential safety hazards from construction sites [7; 8; 9]. To prevent workers' exposure to unsafe conditions, OSHA requires construction projects to deploy safety experts called \"competent persons\" who can detect existing or predictable safety hazards and have the authority to correct them [30]. The competent person's roles include observing conditions and activities of the construction site, identifying potential safety hazards, and correcting problematic conditions or behaviors. Like safety monitoring, construction safety planning is also an essential task in proactively eliminating potential hazards before construction starts. During safety planning, locations and times of potential safety hazards should be thoroughly identified manually [31] or automatically [32; 33]. Highway and bridge construction projects create project-specific safety planning called Internal Traffic Control Plans (ITCPs) to direct construction traffic in work zones and separate heavy equipment from workers on foot [6]. However, even with proactive safety planning, onsite activities still require frequent site visits followed by a labor-intensive visual analysis that can be highly error-prone. Similarly, an ITCP presents a static plan that requires site visits and manual observation. The execution of the static ITCP can potentially benefit by incorporating real-time locations of workers, equipment, and vehicles that dynamically move during construction. To overcome the significant limitations of traditional manual safety monitoring, recent studies have proposed the use of sensing technologies. The use of sensing technologies aims to enable real-time communication through automated, continuous, and accurate monitoring of construction site conditions. [PERSON] et al. [14] implemented construction safety management using building information modeling (BIM), RFID sensors, and cloud communication. The proposed solution was able to divide the environment into different zones and track the presence of workers inside the zones. The coarse localization provided by this solution can be used for some safety applications; however, it does not fulfill all requirements such as proximity detection. [PERSON] et al. [34] used ultrasonic and infrared sensors to create another automatic safety monitoring system. They used a mobile sensing device to alert workers (without sensor tags) approaching predefined hazardous areas in construction sites. However, the functionality of the system only relied on proximity estimation between the workers and sensing devices. This means that it did not provide construction and safety managers with comprehensive information about the activities of workers and the construction environment. [PERSON] et al. [10] created a Bluetooth low energy (BLE)-based indoor localization solution to monitor workers in a building. In their work, they used 40 BLE beacons to cover a 27 \(\times\) 39 m field. They later improved the accuracy of their localization method by fusing the output of the localization with motion sensors and building geographic information [11]. The first challenge with this approach is the deployment of localization infrastructure. Placing a large number of BLE beacons through the whole area is not plausible in all construction sites (e.g., it is impossible to place a beacon in the middle of the road where trucks and loaders are passing). Furthermore, fusing data from multiple sensors for localization is not practical in all entities. For example, tracking an excavator with sophisticated movements (e.g., rotation, displacement) is only feasible if the movements are limited, which does not apply to all construction sites. Researchers have found UWB-based systems to demonstrate high potential for localization technology. [PERSON] et al. [12] developed a prototype for proactive safety management and real-time alert of potential overhead hazards using UWB technology.