Quantitative Comparison of System Architectures for an SAE Level 4 Highway Pilot

The development of SAE Level 4 autonomous driving systems requires fault-tolerant architectures to ensure proper operation and robustness under demanding operational conditions. These architectures must gracefully handle hardware and software faults to maintain system functionality for a minimum operational timeframe, ensuring a fail-operational capability. The selection of an appropriate system architecture is crucial for managing the complexity of autonomous driving systems while achieving effective and efficient fault tolerance. This paper presents a preliminary quantitative comparison of different system architectures—symmetric and asymmet-ric—for a reference use case of an SAE Level 4 Highway Pilot. Specifically, we evaluate a Triple Modular Redundancy symmetric architecture, a Channel-Wise Doer/Checker/Fallback asymmetric architecture, and a Layer-Wise Doer/Checker/-Fallback asymmetric architecture. The comparison leverages Stochastic Activity Networks (SAN) modeled in the Mobius tool to assess key dependability metrics, particularly safety and reliability. Our preliminary results provide initial insights into the differences between symmetry and asymmetry in faulttolerant designs, highlighting their potential impact on safetycritical autonomous driving systems. This work contributes to a deeper understanding of architectural trade-offs in the design of dependable autonomous systems and provides guidance to system designers in making informed architectural decisions while strengthening safety argumentation.