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Section 4: Subway

The subway, built underground in cities, belongs to the heavy-rail transit system with a relatively heavy axle load. It uses steel rail and wheel systems, capable of transporting over 30,000 passengers per hour during peak times. Mostly underground but can also be at-grade or elevated based on city needs. With dense station spacing, electric power, fully enclosed lines, and automated signal control, the subway boasts large capacity, high speed, safety, punctuality, comfort, low pollution, and land conservation. However, it has high construction costs and can be difficult to evacuate passengers during disasters like fires. It falls under general railway but solely transports passengers, differing from conventional railways in power supply (third-rail, DC 750V-1500V) and signal control systems similar to high-speed rail for safe, dense, and frequent operations.

Ventilation and environmental control systems are essential due to its underground locations, addressing heat build-up and ensuring air quality. These include ventilation shafts, smoke control, emergency ventilation, and air conditioning.

China's subway uses the standard gauge of 1435mm with heavy-duty rails and either ballast or concrete beddings. Subway stations, vital for the underground transit system, are designed based on local economic levels and passenger needs. Stations are similarly spaced to bus stops, with functional architecture. Luxury decorations are unnecessary as stations are for quick passenger transit, unlike shopping malls. Stations are classified by operation (intermediate, terminal, transfer, and turnaround) and structure (underground, at-grade, and elevated). Platforms are either side or island types, with island platforms being more common for easy passenger transfer and gathering.

Subway trains are electric, self-propelled, with motor-equipped cabs at both ends. They are typically 4-8 cars long, 3m wide, requiring quick acceleration/deceleration, short braking distances, and high speeds. Carriages are made of fire-resistant materials.