In most modern railway systems, the train cars are not "fixed" to the wheels in the way a car body is attached to its chassis. Instead, the car body sits on a specialized assembly called a bogie (or truck). The bogie contains the wheels, axles, suspension, and often the braking system and motors. The train car is connected to the bogie via a center pivot or "kingpin" and a series of "side bearings" and springs. This allows the bogie to rotate independently of the car body, which is essential for the train to navigate tight curves at high speeds without the wheels binding or derailing. In many high-speed trains like the Shinkansen or TGV, "articulated" designs are used where two cars share a single bogie between them. This system provides a much smoother ride and improved safety, as the car's weight is distributed across the heavy-duty bogies, which are effectively "independent" vehicles that carry the car body along the tracks.