# Smart Intersections and Connected Autonomous Vehicles for Sustainable Smart Cities: A Brief Review
## 3 Integrated Technologies for Smart Roads and Intersections  
Smart roads form the backbone of intelligent transportation systems, enabling connected, efficient, and sustainable urban mobility. These high-tech nodes can be equipped with IoT sensors, Vehicular Communication systems (V2X), and AI-enabled navigation and control networks so that there can be real-time decision-making and dynamically controlled traffic streams on road networks. One of the building blocks of these roads is how they can allow connected and autonomous vehicles (CAVs) to use V2X communication, which includes infrastructure communication (V2I), vehicle-to-vehicle communication (V2V), and vehicle-to-pedestrian communication (V2P) (Figure 2). These coupled systems improve situational awareness and streamline traffic flow, making roads safer by using high-precision technologies, including LiDAR/millimeter-wave radar/edge computing for real-time analytics [4]. V2X technology enables predictive traffic control, risk detection in advance, and synchronized traffic light management through exchanging information without significant delays. They also contribute to fulfilling the sustainability goal of lowering traffic congestion and carbon emissions. IoT sensors are embedded into the road, continuously surveilling traffic density, vehicle speeds, and traffic conditions, providing input data to AI-driven traffic management systems that respond to signal timing and lane allocation using real-time data [5,6]. Research has shown that these responsive control methodologies substantially reduce fuel usage and greenhouse gas emissions, further proving the environmental role of dynamically connected transportation networks [11, 12, 13, 14, 15, 16, 17, 18, 19]. One of the critical functions of innovative roads is real-time infrastructure monitoring, which enhances the durability, performance, and robustness of transportation networks. Roads with connected sensors to measure the road pavement condition [5] can detect surface deterioration [20, 21, 22], structural fatigue [23], and environmental wear marks [24, 25]; therefore, road operators can take preventive maintenance strategies and be aware of repair costs. Using these data, AI-powered predictive maintenance models predict infrastructure failures before they happen to aid in the long-term sustainability of roadways. High-tech roads also amalgamate renewable energy systems such as solar-powered roads, kinetic energy harvesting, etc., which encourage urban sustainability as they reduce the reliance on traditional energy sources [26, 27]. Adaptive road infrastructure and IoT-enabled intersections work together in an intelligent mobility ecosystem. According to the PIARC [28], smart roads can be classified based on their capabilities to host CAVs, which can be determined with the interaction of two indicators: the Level of Service for Automated Driving (LOSAD) and the Infrastructure Support for Automated Driving (ISAD). The LOSAD indicates the physical readiness of the road segment to support  
Figure 2: Examples of technologies used in smart intersections. automation, whereas the ISAD represents the connectivity support. The following types of roads are therefore considered [28]:  
* Human way: the road infrastructure is not able to host CAVs. * Assisted way: the road infrastructure is adequate to perform autonomously, but this condition may stop due to several causes. * Automated way: the infrastructure exhibits reasonably good connectivity and physical infrastructure capabilities, so disengagements or takeover requests would be lower compared to the Assisted way and Human way. * Fully Automated way: the road presents a continuous Operational Road Section (ORS), ensuring Operational Design Domain (ODD) compatibility with most level 3-4 vehicles. * Autonomous way: Similarly to the Fully Automated way, the connectivity infrastructure supports cooperative driving, so the infrastructure can receive and transmit tailored instructions to all vehicles, micromanaging traffic performance.