In railway engineering, cant deficiency is defined in the context of travel of a rail vehicle at constant speed on a constant-radius curve. Cant itself refers to the superelevation of the curve, that is, the difference between the elevations of the outside and inside rails. Cant deficiency is present when a rail vehicle's speed on the curve is greater than the speed at which the components of wheel to rail force are normal to the plane of the track. In that case, the resultant force (aggregate gravitational and centrifugal force) exerts on the outside rail more than the inside rail, in which it creates lateral acceleration toward the outside of the curve (which could lead to tipping or derailing). In order to reduce cant deficiency, the speed can be reduced or the superelevation can be increased. The amount of cant deficiency is expressed in terms of required superelevation to be added in order to bring the resultant force into balance between the two rails. On the contrary, it is said to be "cant excess" if the resultant force exerts more against the inside rail than the outside rail, for instance, a high superelevation curve with a train traveling at a low speed. Forces The forces that bear on the vehicle in this context are illustrated in the following figure. A vehicle's motion at speed along a circular path embodies centripetal acceleration of magnitude toward the center of the circle, the curvature of that path being where is the radius of the circle. This centripetal acceleration is produced by horizontal forces applied by the rails to the wheels of the vehicle, directed toward the center, and having sum equal to where is the mass of the vehicle. The net horizontal force producing the centripetal acceleration is generally separated into components that are respectively in the plane of the superelevated (i.e., banked) track and normal thereto. The component normal to the track acts together with the much larger component of gravitational force normal to the track and is generally neglected. It can slightly increase the vertical load seen by the vehicle suspension but it does not create lateral acceleration as perceived by passengers and does not cause lateral deflection of the vehicle suspension. The track is superelevated so that the component of the acceleration of gravity in the plane of the track will provide some fraction of the horizontal acceleration in the