When a vehicle travels around a horizontal curve it is sometimes necessary to tilt the road upwards to minimise the risk of the car running off the road at speed. This tilting of the road is referred to as superelevation. In practice if steep superelevations were introduced to roads they could be alarming to drivers approaching them and dangerous with reduced speeds. Therefore in rural areas superelevation is limited to 7% and in urban areas superelevation is limited to 5%.
In order to achieve the desired superelevation a road must go from its normal cross section to a super elevated cross section in order to do this the cross section goes through 2 main stages. Tangent Runout and Superelevation Runoff.
Once the road has passed through a sufficent portion of the curve the Superelevation Runoff and Tangent Runout are reversed and the road returns to its normal cross section.