Rail Cant
Cant (also called superelevation)
When a train (or any vehicle) goes around a curve there is a force (centrifugal) which
causes the vehicle to move towards the outside rail and if not countered by an opposing force
(centripetal) the outside wheel flange would grind up the rail with the possibility of a derailment.
To create this opposing centripetal force a curved section of track will have the plane
of the rail bed tipped slightly so that it slopes downward toward the inside of the curve.
Equilibrium speed is the speed at which the centrifugal force developed during the
movement of the vehicle on a curved track is exactly balanced by the centripetal
force provided by the cant.
Cant is often described as the height of the outside rail above the inside rail on a
curved section of track but it's important to note that this additional height isn't created
simply by putting spacers underneath the outside rail. The plane of the entire rail
bed including sleepers and gravel base is rotated by a calculated amount with the
slope towards the inside rail.
Thus, the conical faces of the wheels still present the same angle to the rail head.
(Note that in this image the rail inclination is achieved through molded concrete
sleepers. Wooden sleepers require special angled plates to be inserted beneath
the rails.)
[Image Credit]
"Cant", "superelevation", and "crosslevel" all describe the same thing - the condition
of the outside rail on a curve (usually) being higher than the inside rail. Cant seems
to be the term used in American railroading and is measured in inches. Superelevation is
described as being an angle expressed in degrees. ( But I find the literature
to be confusing with some sources referring to superelevation and crosslevel some-
times in inches and at other times as a ratio or angle.)
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The degree of cant (superelevation) is dependent on at least the following things:
The radius of the curve
The expected class of rail vehicles (freight, passenger). This helps determine
the mass of the vehicle.
The anticipated speed of the vehicle
A simplified formula to determine the Equilibrium Elevation is
G = Gauge of track in feet.
v = Velocity in feet per second.
g = Acceleration due to gravity taken as 32.16 feet per second per second.
R = Radius of center line of curve in feet.
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