Shaping the future of transit: Innovations and prospects of intelligent connected bus systems

As urbanization progresses, traffic congestion has become an increasingly severe issue confronting metropolitan areas worldwide. Intelligent connected bus systems (ICBS) emerge as a transformative solution to address this challenge. This review synthesizes ICBS as a layered closed-loop transit system that links infrastructure, intelligent buses, and operation platforms through continuous vehicle-road-cloud coordination. We first summarize its system architecture, including centralized operation platforms, smart intersections, smart bus stops, and intelligent connected buses, and explain how connectivity is translated into operational control. We then review two technical pillars under real-world deployment constraints: safety-oriented advanced driver assistance systems, covering cooperative perception, speed-signal coordination, and bus-oriented motion planning; and reliability-oriented intelligent scheduling, covering electrified fleet and charging management, automation-enabled dispatching, and fixed-flexible services. Finally, we discuss the transition toward precise public transit and highlight key challenges in system-level performance verification, robustness under uncertainty, infrastructure affordability and legacy integration, multi-purpose service integration and deployment, and bus-specific automated driving. Overall, ICBS should be understood as a service-oriented operational paradigm that enables more adaptive, reliable, and sustainable urban public transport.