Understanding Safety Goals in Automotive Functional Safety (ISO 26262) for ADAS

Introduction

In the context of automotive functional safety, a safety goal is a specific criterion that must be met to ensure the safety of the vehicle's occupants, other road users, and the environment. These goals are derived from the identification and analysis of potential hazards associated with the operation of the vehicle and its systems. Safety goals are a fundamental part of the ISO 26262 standard, which provides guidelines for ensuring the functional safety of electrical and electronic systems in vehicles.

Importance of Safety Goals

Safety goals are crucial for ADAS (Advanced Driver Assistance Systems) because these systems rely heavily on complex electronic and software components that must function correctly to ensure safety. Failure to meet safety goals can lead to accidents, injuries, or fatalities. Therefore, defining clear and measurable safety goals is essential for designing, developing, and testing ADAS systems.

Process of Defining Safety Goals

1. Hazard Analysis and Risk Assessment (HARA):

• Thorough Analysis: HARA involves a comprehensive examination of potential hazards associated with the vehicle and its ADAS features. This analysis aims to identify all possible scenarios that could lead to harm or danger.

• Environmental Conditions: Factors such as weather conditions, road conditions, and lighting are considered. For example, poor visibility due to fog or heavy rain could increase the risk of accidents if not properly addressed by ADAS features.

• System Failures: The analysis includes identifying possible failures or malfunctions in the vehicle's systems, including the ADAS components. This helps in understanding the risks associated with system errors and how to mitigate them.

• Human Factors: HARA considers the influence of human behavior on the operation of the vehicle and its ADAS features. This includes driver distractions, fatigue, and response times, which can impact the effectiveness of ADAS systems.

• Risk Assessment: Once hazards are identified, a risk assessment is performed to determine the severity and likelihood of each hazard. This helps prioritize which hazards need immediate attention and mitigation.

• Mitigation Strategies: Based on the analysis and risk assessment, mitigation strategies are developed to reduce the risks associated with identified hazards. This may include design changes, safety features, or operational procedures.

• Documentation: HARA results in the documentation of all identified hazards, their associated risks, and the mitigation strategies proposed. This documentation serves as a reference for future safety assessments and design improvements.

2. Identification of Safety Goals:

• HARA Results: The Hazard Analysis and Risk Assessment (HARA) process provides insights into potential hazards and their associated risks. These insights are used to formulate specific safety goals.

• Mitigation of Risks: Safety goals are aimed at reducing or eliminating the risks identified in the HARA. This may involve enhancing the system's ability to detect hazards, implementing features to mitigate the effects of hazards, or developing strategies to avoid hazards altogether.

• Specificity: Safety goals are precise and specific, addressing each hazard identified in the HARA. For example, a safety goal could be to ensure that the ADAS system can detect pedestrians in low-light conditions to mitigate the risk of collisions.

• Measurability: Safety goals are formulated in a way that allows them to be measured or evaluated. This enables engineers to assess whether the system meets the specified safety requirements.

• Functional Requirements: Safety goals often translate into functional requirements for the system. These requirements define what the system must do to achieve the safety goals, such as the response time for detecting a hazard or the accuracy of the detection mechanism.

• Traceability: Safety goals should be traceable back to the hazards identified in the HARA. This ensures that each safety goal is directly linked to a specific hazard and its associated risk.

• Iterative Process: The identification of safety goals is not a one-time activity. It is an iterative process that may evolve as new hazards are identified or as the system's design and functionality change.

3. Derivation of Safety Requirements:

• From Goals to Requirements: Safety requirements are derived directly from the safety goals identified in the previous steps. These requirements translate the abstract safety goals into specific, actionable directives for the system design.

• Functional and Non-functional Characteristics: Safety requirements encompass both the functional aspects of the system (what it must do) and the non-functional aspects (how it must perform). For example, a safety requirement might specify the response time for a collision avoidance system (functional) or the reliability of a sensor (non-functional).

• Detail and Precision: Safety requirements are detailed and precise to ensure that they can be implemented effectively. They often include specific parameters, tolerances, and performance criteria that must be met.

• Hierarchy and Relationships: Safety requirements are often organized hierarchically, with higher-level requirements decomposed into lower-level ones. This hierarchy helps to establish relationships between different requirements and ensures that they are consistent and coherent.

• Compliance and Verification: Safety requirements serve as a basis for verifying that the system complies with safety goals. Verification processes, such as testing and analysis, are used to ensure that the system meets all safety requirements.

• Documentation: Safety requirements are documented to provide a clear and comprehensive specification for system development. This documentation is essential for communication between stakeholders and for ensuring that the system is developed correctly.

Examples of Safety Goals for ADAS

2. Automotive Emergency Braking (AEB):

• Hazard: Collision with obstacles.

• Risk: High severity.

• Safety Goal: Ensure that the AEB system can detect obstacles in the vehicle's path and apply the brakes to avoid or mitigate collisions.

• Safety Requirement: The AEB system shall detect obstacles within a specified range and apply the brakes with a specified force to avoid collisions.

2. Lane Keeping Assist System:

• Hazard: Unintended lane departure.

• Risk: Moderate severity.

• Safety Goal: Ensure that the Lane Keeping Assist system can assist the driver in safely maintaining the vehicle within the lane boundaries.

• Safety Requirement: The Lane Keeping Assist system shall provide steering input to keep the vehicle within the lane if the driver unintentionally departs from the lane.

3. Adaptive Cruise Control (ACC) System:

• Hazard: Rear-end collision due to inadequate following distance.

• Risk: High severity.

• Safety Goal: Ensure that the ACC system can maintain a safe following distance from the vehicle ahead under varying driving conditions.

• Safety Requirement: The ACC system shall adjust the vehicle's speed to maintain a minimum following distance from the vehicle ahead.

3. Blind Spot Detection System:

• Hazard: Collision due to undetected vehicles in blind spots.

• Risk: High severity.

• Safety Goal: Ensure that the Blind Spot Detection system can detect vehicles or objects in the vehicle's blind spots and provide timely warnings to the driver.

• Safety Requirement: The Blind Spot Detection system shall monitor the vehicle's blind spots and provide visual or audible warnings to the driver if a vehicle is detected.

4. Traffic Sign Recognition System:

• Hazard: Incorrect interpretation of traffic signs.

• Risk: Moderate severity.

• Safety Goal: Ensure that the Traffic Sign Recognition system can accurately detect and interpret traffic signs to provide relevant information to the driver.

• Safety Requirement: The Traffic Sign Recognition system shall correctly recognize and interpret traffic signs and display the relevant information to the driver.

Conclusion

Safety goals are a critical component of automotive functional safety, especially for ADAS systems. They provide specific targets for ensuring the safe operation of these systems and are derived from a systematic analysis of potential hazards. By defining clear safety goals and implementing appropriate safety requirements, automotive manufacturers can enhance the safety and reliability of ADAS systems, contributing to overall road safety.

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