graph TD
    A["Traffic Problems in Singapore"]
    B["Solutions"]
    A --> B
    B --> C["Downtown Access Control"]
    B --> D["Car Purchase Restrictions"]
    B --> E["Public Transportation"]
    
    C --> C1["Special pass required"]
    C --> C2["Must display on windshield"]
    
    D --> D1["Certificate requirement"]
    D --> D2["Limited certificates"]
    D --> D3["High tax on cars"]
    D --> D4["3-4x cost vs US/Canada"]
    
    E --> E1["Excellent subway system"]
    E --> E2["Good taxi service"]
    E --> E3["Efficient bus system"]