Fault Tolerance and Fallback Strategies in Connected and Automated Vehicles: A Review

Connected and Automated Vehicles (CAVs) are considered the future of transportation, offering increased safety, efficiency, and convenience. However, their reliance on sophisticated sensors and complex algorithms poses challenges, especially in scenarios with uncertainties, constraints, or failures. Dynamic Driving Task (DDT) fallback and fault tolerance strategies serve as critical mechanisms to ensure safe operation when primary systems fail or face functional insufficiencies. This paper provides an analysis of the fault-related taxonomy established by international standards and a comprehensive review of the DDT fallback and fault tolerance strategies used in CAVs, focusing on their strategy, classification, and implementation methods. Moreover, the challenges and future research directions for the development and improvement of fault tolerance strategies are discussed. The analysis shows that the main trends are to avoid the termination of the CAV operation in case of a failure or functional insufficiency, or at least to be able to guide the vehicle to a safe state. However, there is a tendency towards the possibility of continuing the operation. This review contributes to a deeper understanding of the role of DDT fallback and fault tolerance strategies for CAVs and future trends.