## 4 Control Mechanism Transformation in New Heterogeneous Traffic Flow Environments on Urban Roads
### Traffic Control Mechanisms for Isolated Intersection Scenarios  
As the basic unit of urban road networks, isolated intersections form the foundation of intelligent connected traffic control research. Leveraging the heterogeneous traffic flow characteristics established in Section 4.2, intelligent connected environments enable expanded control objectives. The mixed-operation challenges and penetration rate considerations previously discussed now inform specific control mechanism design. Safety-critical control mechanisms represent an important research direction for intelligent connected isolated intersection control. With the emergence of heterogeneous traffic conditions, traffic safety faces new challenges. [PERSON] et al. proposed a Safety-critical Traffic Control (STC) strategy enabling intelligent connected vehicles to simultaneously maintain safe distances with both preceding vehicles and following human-driven vehicles [44]. This research innovatively applies Control Barrier Functions (CBFs) to provide formalized safety guarantees of collision-free behavior for closed-loop systems, validating the method's effectiveness in achieving provably safe traffic through extensive numerical simulations. This approach is particularly suitable for heterogeneous traffic environments with low intelligent connected vehicle penetration rates, minimizing deviations from nominal stabilizing controllers while ensuring safety. Regarding adaptive signal optimization, traditional fixed-time signal control struggles to address dynamic traffic demands. To tackle this issue, [PERSON] et al. developed an adaptive signal controller based on Approximate Dynamic Programming (ADP), achieving three operational objectives: dynamic green time allocation, automatic control parameter adjustment, and rapid signal plan revision [45]. This method alleviates computational burdens by using approximations of dynamic programming value functions and reinforcement learning to update approximations, achieving substantial vehicle delay reductions compared to optimized fixed-time plans in computer simulations. This near-real-time processing capability provides important support for dynamic signal control in intelligent connected environments. Schedule-driven collaborative control represents a frontier direction for isolated intersection control. The cooperative schedule-driven intersection control method proposed by [PERSON] et al. combines intelligent connected vehicles with intersection scheduling agents, optimizing platoon arrival times through wireless communication to adjust vehicle speeds, thereby reducing cumulative delays [46]. This method's core lies in establishing closed-loop feedback mechanisms between intersection schedulers and vehicles, not only optimizing signal timing but also actively adjusting vehicle behavior to achieve overall system collaboration. This research demonstrates that by leveraging the communication and automation capabilities of intelligent connected vehicles, decentralized schedule-driven traffic control can improve traffic flow efficiency in complex urban road networks. Flexible facilities and reservation control provide entirely new approaches for isolated intersection intelligent connected control. [PERSON] et al. conducted a systematic review of intersection control in intelligent connected environments, focusing on analyzing the development status and limitations of two major categories of methods: intelligent connected vehicle trajectory planning and joint intersection control [47]. Building upon this foundation, [PERSON] et al. proposed the Combined Flexible Lane Assignment and Reservation-based Intersection Control (CFLARIC) concept, offering comprehensive lane assignment possibilities with appropriate reservation-based intersection control [48]. In simulation testing, this method demonstrated clear advantages in both efficiency (delays and stop frequency) and safety (reduced conflict situations) compared to traditional fixed-time control and basic reservation control.