The superelevation is the right-angled slope of the road surface and is part of the horizontal curve design. Driving through a curve at too high speeds can create too high centrifugal forces causing a vehicle to skid (if the skid resistance is also too low) or to roll over. In combination with other curve design components like the curve radius and pavement friction, the superelevation decreases the risk of skidding or rolling over for vehicles driving through the curve at the design speed. Apart from reducing the risk of skidding or rolling over, the superelevation provides for water runoff. The superelevation can also increase crash risk when it is too high. It can cause vehicles too slide or roll over inwards toward the curve. The risk of such an event increases given the combination of too high superelevation rates, vehicles driving slowly, road being slippery or on combinations of horizontal curves and vertical grades. Four coded studies all found that superelevation deficiencies relate to an increase in crashes at curves. Passenger vehicles were found to be more prone to skidding than rolling over. Heavy good vehicles on the other hand were found to be prone to rolling over due to a relatively high centre of mass. Also, the studies indicated that taking operational speeds into account in the design and evaluation of curves will result in a more robust curve design. On the basis of these results, it is expected that the measure of improving superelevation will have analogous positive effects on road safety.
Superelevation deficiencies at curves
European Road Safety Decision Support System, developed by the H2020 project SafetyCube
European Commission, Brussels