Cant (road/rail)

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The cant of a road (sometimes referred to as camber) or railway (also referred to as superelevation) is the difference in elevation of the two edges; a cant which is not equal to zero results in a banked turn, allowing vehicles traveling through the turn to go at higher speeds than would normally be possible.

1 Rail
- 1.1 Examples
2 Roads
3 See also

[edit] Rail

In the case of railways, the cant helps a train steer around a curve and keeps the inside wheel edges from touching the rails, minimizing wear and tear.

The amount of cant has to be chosen for a given speed, so that if trains travel through the turn at a different speed, the cant ceases to serve its initial purpose and will actually lead to damage to the wheels. As a result, a compromise value of cant must be chosen when turns are designed.

The maximum value of cant (the height of the outer rail above the inner rail) for a standard gauge railway is about 6 inches (150mm).^{[citation needed]}

Ideally, the track should have railroad ties (sleepers) at an increased rate per mile, and a greater depth of ballast to accommodate the increased forces exerted by the train.

When a straight becomes a curve, the amount of cant cannot change from zero to its maximum immediately. Rather, the cant must change (ramp) gradually in a track transition curve. The length of the transition curve depends on the maximum speed on the line – the higher the speed, the greater length is required. The main functions of cant are

to have a better distribution of loads on both rails
to reduce the wear and tear of rails and rolling stock
to neutralize the effect of lateral forces
to provide comfort to passengers

[edit] Examples

In Australia, ARTC is increasing speed around curves sharper than 800 m radius by replacing wooden sleepers with heavier, concrete ones so that the cant can be increased.

[edit] Roads

In the case of roads, cant also helps rainwater drain from the road surface. In civil engineering, cant is often referred to as superelevation, which is a strong factor in the design of a road based on its design speed.