Study of rail vehicle dynamics with analytical models dates back as early as the first half of nineteenth century. Rail vehicle dynamics as a topic of research has gained momentum after pioneering work has been done by eminent researchers in the field to reveal the importance of mechanics of contact between wheel and rail. Railways, being most popular mode of transport there is an everincreasing demand for higher speed, improved ride comfort and smooth operating conditions at less cost. As the speed of rail vehicle increases, a speed, called critical speed is reached when the vehicle system has zero damping and beyond that speed the motion is associated with sustained periodic oscillations. A railway vehicle becomes unstable beyond a critical speed. This instability results in violent lateral vehicle oscillation. Such instability arises because of speed dependent forces and moments at the rail-wheel contact surfaces. Often rail passenger vehicles are required to negotiate tight curves. During curve negotiation most of the time there is flange contact associated with large lateral slip, which results in tremendous wear and tear and also objectionable noise at the contact surfaces. In an attempt to have an all-inclusive model of railway vehicle a module (called capsule) based bond graph model of rail vehicle is created. It has three main sections namely; the wheelset model, the truck model and the vehicle model. This study leads to the determination of the critical speeds for a free wheelset, truck and vehicle. Simulations of wheelset model, truck model and vehicle model are done individually to study the curving performance. The models are simulated on rigid track and on flexible track also. While modeling the wheelset, basic components of the rail vehicle system no linearity approximations are made so that the model reflects the true dynamic behaviour.