## 4 SAE Levels of Autonomy and V2X  
_SAE Levels of Autonomous Vehicles_  
Advanced driver assistant systems (ADAS) and automated driving systems are classified into various levels of autonomy based on their maturity and capability of handling complex driving scenarios with or without the contribution of the human driver. This classification is widely accepted by regulatory bodies and industry representatives, however, definitions are only addressing the functionalities of the final products, but do not address the capability requirements of the individual components building up the systems. The definition of the levels of autonomy was first introduced by the National Highway Traffic Safety Administration (NHSTA) in 2013 [41]. The proposal was later revised and completed by the Society of Automotive Engineers in the scope of the J3016_201609 taxonomy. The L0-L5 levels of autonomy have since became a standard for assessing the levels of automated systems within and beyond automotive applications [42]. This taxonomy has also been applied in the literature for fields closely related to automated driving, such as urban air mobility [43] and automated surgical procedures [44; 45]. * _LoA 0: No driving automation_ The vehicle does not possess the capability to carry out any automated actions. However, it can still transmit warning signals to the human operator. This limitation underscores the crucial role of human oversight and decision-making in the operation of the vehicle. Despite advancements in automation and vehicle intelligence, the presence of a human operator remains essential to ensure safety and manage complex situations that may arise. By receiving warning signals, the human operator can stay informed about potential hazards or critical events, allowing them to intervene and take appropriate actions as necessary. The integration of warning systems with human-machine interfaces becomes crucial to effectively communicate critical information and enable timely responses for the human operator. Thus, while the vehicle lacks autonomous actuation abilities in these use-cases, it emphasizes the continuous importance of human involvement and situational awareness in ensuring safe and reliable vehicle operation. * _LoA 1: Driver assistance_ ADAS functionalities are enabled, primarily through automated control of either longitudinal (acceleration and deceleration) or lateral (steering) motions. However, it is important to note that the human operator is responsible for the overall control and operation of the vehicle. While the automated system assists in specific aspects of the driving task, such as maintaining a set speed or keeping the vehicle within its lane, the human operator retains the ultimate responsibility for monitoring the driving environment and making critical decisions. * _LoA 2: Partial driving automation_ The vehicle is empowered with the ability to be fully actuated by an autonomous system, enabling coordinated longitudinal and lateral control. The human operator remains actively engaged and responsible for overseeing the driving task. Their continuous involvement is essential to ensure a prompt and seamless transition of control when necessary. Nevertheless, the human operator's active engagement is pivotal. They must be ready to intervene and resume control of the vehicle immediately if the autonomous system encounters limitations or fails to handle certain driving situations. Effective monitoring of the driving environment, awareness of system capabilities and limitations, and the ability to respond promptly to unexpected scenarios are crucial aspects of the human operator's role in Level 2 automation. * _LoA 3: Conditional automation_ The dynamic driving task is primarily managed by the automated system. The human operator is actively supervising the system's operation. The automated system possesses advanced capabilities for environment recognition, decision-making, and control, enabling it to handle the entire driving task under specific conditions.