car

In railway terminology, a car is any vehicle that runs on rails as part of a train consist. The term encompasses both powered and unpowered rolling stock, though in North American usage it more often refers to unpowered cars hauled by a locomotive. A car rides on two or more axles fitted with flanged wheels that grip the rails; the basic four-wheel design uses two axles, while longer cars may have three or more. The car body rests on a frame, which in turn sits on the truck assemblies (bogies) that provide the suspension and wheel assemblies.

Cars are classified by their cargo or function: freight cars (boxcars, flatcars, gondolas, tankcars, hoppers) constitute the largest category; passenger cars carry fare-paying travelers and include coaches, sleeping cars, and dining cars; specialized cars serve specific industries such as auto carriers, refrigerated cars, or depressed-center cars for heavy loads. A standard North American freight car has interior dimensions around 40 to 60 feet long with payload capacity from 30 to 130 tons depending on type. Coupling systems (knuckle couplers on freight cars, draft gear assemblies) absorb shock between units and distribute pulling force through the train consist.

Construction and weight

Car bodies have historically been built from wood, but since the mid-twentieth century steel and aluminum dominate. The underframe is typically a welded steel structure; the car body (sides, roof, floor) may be riveted, welded, or bolted to it. Weight distribution matters greatly: a loaded car must keep wheel loads within rail design limits (often 30 to 35 tons per axle maximum), so heavier cars typically use more axles. Draft gear, usually a combination of steel springs and elastomers, sits between the truck and the car body to isolate shocks from coupling impacts.

Operational issues arise from age, corrosion, and wear. Wood-framed cars, though largely retired, occasionally appear on heritage lines; modern cars face fatigue from thousands of coupling cycles. Wheel flange wear, truck suspension deterioration, and brake component failures represent common maintenance demands. Cars are regularly weighed at interchange points and inspected for safety defects; a car failing inspection is pulled from service until repairs are completed.

The term car itself derives from the Latin carrus, a wheeled vehicle. In British English, freight cars are more often called wagons, while the word car typically refers to passenger vehicles; in North American usage, car applies across both categories. The distinction between car and locomotive is functional: a locomotive has its own prime mover and controls the consist, while a car is a passive component within it. A multiple-unit train (common in electrified commuter and metro systems) blurs this line, as each car carries traction motors, though they still operate as an integrated set rather than independently.