Cant (road and rail)

The cant of a railway track or camber of a road (also referred to as superelevation, cross slope or cross fall) is the rate of change in elevation (height) between the two rails or edges of the road.

This is normally greater where the railway or road is curved; raising the outer rail or the outer edge of the road creates a banked turn, thus allowing vehicles to travel round the curve at greater speeds than would be possible if the surface were level.

In curved railway tracks, the outer rail is elevated, providing a banked turn.

This allows trains to navigate curves at higher speeds and reduces the pressure of the wheel flanges against the rails, minimizing friction and wear.

The main functions of cant are the following: On horizontal curves, curvature causes a centrifugal force acting outward on the outer wheel.

Generally the aim is for trains to run without flange contact, which also depends on the tire profile of the wheels.

Slower trains will tend to make flange contact with the inner rail on curves, while faster trains will tend to ride outwards and make contact with the outer rail.

Many high-speed lines do not permit slower freight trains, particularly with heavier axle loads.

Ideally, the track should have sleepers (railroad ties) 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, where the rails straighten out, the amount of cant cannot change from zero to its maximum immediately.

For the United States, with a standard maximum unbalanced superelevation of 75 mm (3 in), the formula is this: where

[citation needed] For high-speed railways in Europe, maximum cant is 180 mm (7 in) when slow freight trains are not allowed.

The maximum value for European railways varies by country, some of which have curves with over 280 mm (11 in) of unbalanced superelevation to permit high-speed transportation.

In the approximation it is assumed that the cant is small compared to the gauge of the track.

as the maximum allowed additional amount of cant that would be required by a train moving faster than the speed for which the cant was designed, setting the maximum allowed speed

In the United States, maximum speed is subject to specific rules.

and the conversion factors for US customary units, the maximum speed of a train on curved track for a given cant deficiency or unbalanced superelevation is determined by the following formula: with

[4] In civil engineering, cant is often referred to as cross slope or camber.

Along straight or gently curved sections, the middle of the road is normally higher than the edges.

This is called "normal crown" and helps shed rainwater off the sides of the road.

During road works that involve lengths of temporary carriageway, the slope may be the opposite to normal – for example, with the outer edge higher – which causes vehicles to lean towards oncoming traffic.

The amount of superelevation increases with its design speed and with curve sharpness.

[18][19][20][21] In cyclocross, off-camber sections are very common as the courses snake around ridges, adding difficulty.