Autonomous public transport is becoming an integral component of the Smart City paradigm and, concurrently, a key element of critical urban infrastructure. Besides operational benefits, increasing automation, connectivity, and digitalization introduce updated requirements for security, reliability, and resilience against cyberattacks and unintended system behaviors. This article presents a methodological and technological framework for deploying autonomous public transport management in urban environments, with a special emphasis on rail-based modes and their safe integration into a city's critical infrastructure. The proposed approach combines dynamic HD maps, a digital twin of the urban environment, and cooperative intelligent transport systems (C-ITS) to achieve precise localization, enhanced situational awareness, and real-time data exchange among vehicles, infrastructure, and dispatch centers. Vehicle and infrastructure sensors feed a unified data platform that supports monitoring, diagnostics, and operational control. The architecture prioritizes secure data transmission, network segmentation, access control, and cyber-threat mitigation to ensure business continuity and high service availability. Functionality was verified on a pilot section of a real tram line instrumented with infrastructure and onboard sensors; testing occurred under normal operating conditions with driver supervision for maximum safety. The results indicate the feasibility of gradual autonomy introduction while maintaining high levels of safety and compliance with critical-infrastructure requirements. The combination of HD maps, a digital twin, and security-by-design principles significantly improves robustness, interoperability, and resilience to operational and cyber risks.