car door

A car door is a hinged or sliding panel that provides passenger entry and exit on a railway carriage or motor vehicle. On rail stock, it must seal against the body frame to maintain pressurization on high-speed trains and climate control on all passenger services. The door mechanism must function reliably across thousands of cycles over the vehicle's service life, typically 20 to 40 years for mainline rolling stock.

Railway car doors differ significantly from automobile doors in construction and operation. Passenger doors on trains are usually plug-type or sliding designs rather than swing hinges, because swing doors present safety hazards on moving trains and consume aisle space. Plug doors slide inward then along the car body; sliding doors move horizontally only. Both types use pneumatic or hydraulic actuation linked to control systems that prevent operation when the train is moving above a set speed, usually 3 to 5 mph. The door frame must withstand emergency decompression and impacts from platform edges.

Car doors are typically aluminum alloy bodies with rubber or EPDM gaskets around the perimeter. The seal must maintain air pressure differentials of 0.3 to 0.5 psi on high-speed trains and resist moisture ingress in coastal or humid environments. Stainless steel hardware prevents corrosion from salt spray. Window panels are laminated polycarbonate or tempered glass, depending on safety specifications and local regulation.

Failures in car door systems are common wear points. Gasket degradation allows pressure loss and fogging. Actuator seals leak, reducing pneumatic pressure. Mechanical linkages corrode or bind, preventing full closure. On high-frequency urban services, doors may cycle 1,000 times per week, accelerating component wear. Preventive maintenance schedules typically include gasket replacement every 10,000 to 15,000 operating hours and actuator overhaul every 25,000 hours.

The term "car door" in rail context refers specifically to passenger-access doors on coaches or carriage bodies, distinguishing them from engine compartment access panels, equipment boxes, or freight car doors, which have different mechanical and safety requirements. Emergency exits, sometimes called secondary or overwing doors on aircraft, follow different standards but share the same fundamental principle: reliable sealing and controlled operation under operational and emergency conditions.