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Rail
On railways cant helps a train steer around a curve, keeping the wheel flanges from touching the rails, minimizing friction and wear.
The amount of cant must be chosen for a given speed, and if trains traverse the turn at different speeds, the cant ceases to serve its purpose, and can lead to damage. As a result, a compromise value of cant must be chosen during design.
The maximum value of cant (the height of the outer rail above the inner rail) for a standard gauge railway is about 6 inches (150 mm).citation needed
Ideally, the track should have railroad ties (sleepers) at a closer spacing, and a greater depth of ballast to accommodate the increased forces exerted in the curve.
At the ends of a curve, the amount of cant cannot change from zero to its maximum immediately. The cant must change (ramp) gradually in a track transition curve. The length of the transition depends on the maximum allowable speed – the higher the speed, the greater length is required.
The main functions of cant are
- better distribute load across both rails
- reduce rails and wheel wear
- neutralize effect of lateral forces
- improve passenger comfort
Examples
In Australia, ARTC is increasing speed around curves sharper than 800 m radius by replacing wooden sleepers with concrete ones so that the cant can be increased.
Roads
In the case of roads, cant also helps rainwater drain from the road surface. In civil engineering, cant is often referred to as cross slope or superelevation. Cross slope is a strong factor in the design of a road based on its design speed.
See also
