flowchart LR
    A["Reliant on driver judgment —<br/>limited field of view,<br/>limited reaction speed"] --"V2X real-time<br/>communication links"--> B["360-degree situational awareness —<br/>vehicles, infrastructure, pedestrians"] --"Accident prevention,<br/>traffic optimization"--> C["Autonomous-driving safety,<br/>the smart city realized"]

    style A fill:#FFEBEE,stroke:#D32F2F,color:#000
    style B fill:#E3F2FD,stroke:#1976D2,color:#000
    style C fill:#E8F5E9,stroke:#388E3C,color:#000
  

    flowchart TD
    VEH["Vehicle"]

    subgraph R1["　"]
        direction LR
        V2V["V2V<br/>vehicle-to-vehicle —<br/>forward-collision warning,<br/>cooperative emergency braking"]
        V2I["V2I<br/>vehicle-to-infrastructure —<br/>traffic lights, CCTV, RSU —<br/>receiving traffic information"]
        V2P["V2P<br/>vehicle-to-pedestrian —<br/>sharing smartphone location,<br/>preventing crosswalk collisions"]
    end
    subgraph R2["　"]
        direction LR
        V2N["V2N<br/>vehicle-to-network —<br/>cloud/MEC —<br/>maps, OTA updates"]
        V2G["V2G<br/>vehicle-to-grid —<br/>coordinating EV charge/discharge,<br/>linkage to the smart grid"]
    end

    VEH --> V2V
    VEH --> V2I
    VEH --> V2P
    VEH --> V2N
    VEH --> V2G

    style VEH fill:#1E3A5F,stroke:#1E3A5F,color:#fff
    style V2V fill:#E3F2FD,stroke:#1976D2,color:#000
    style V2I fill:#F3E5F5,stroke:#7B1FA2,color:#000
    style V2P fill:#E8F5E9,stroke:#388E3C,color:#000
    style V2N fill:#FFF3E0,stroke:#F57C00,color:#000
    style V2G fill:#FFEBEE,stroke:#D32F2F,color:#000
    style R1 fill:none,stroke:none
    style R2 fill:none,stroke:none
  

    flowchart LR
    subgraph SAFETY["Safety Message System (BSM)"]
        direction TB
        S1["BSM<br/>Basic Safety Message —<br/>position, speed, heading —<br/>broadcast 10x/second"]
        S2["SPAT/MAP<br/>signal phase/timing,<br/>intersection map data,<br/>signal-coordinated driving"]
        S3["RSA<br/>Roadside Alert —<br/>construction, accidents, weather —<br/>hazard-zone notification"]
    end

    subgraph SEC["Security Framework (PKI/V2X Security)"]
        direction TB
        P1["PKI authentication —<br/>pseudonym certificates,<br/>vehicle-identity verification,<br/>privacy protection"]
        P2["Message signing/verification —<br/>prevents tampering,<br/>blocks replay attacks,<br/>ensures integrity"]
    end

    SAFETY --> SEC

    style SAFETY fill:#E3F2FD,stroke:#1976D2,color:#1E3A5F
    style SEC    fill:#FFEBEE,stroke:#D32F2F,color:#B71C1C