The cant of a road (sometimes referred to as camber or cross slope) or railway (also referred to as superelevation) is the difference in elevation between the two edges. A cant which is not equal to zero results in a banked turn, allowing vehicles to traverse the turn at higher speeds than would otherwise be possible.

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).

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

• Cant deficiency
• Tilting train