What is superelevation in roadway design?

Superelevation is a crucial concept in roadway design, particularly when it comes to curves. It refers to the banking or tilting of the roadway surface at a curve, which involves increasing the cross slope of the road to help counteract the effects of centrifugal force that acts on vehicles moving through a curve. By tilting the road, superelevation allows vehicles to navigate the curve more safely and comfortably, reducing the risk of skidding and helping to maintain vehicle stability.

This banking effect is particularly important in ensuring a smooth ride for vehicles, as it allows drivers to maintain better control without excessive reliance on friction. It is designed based on the curve's radius and the intended speed of the vehicles, thus optimizing the roadway's performance.

The other options do not accurately define superelevation. For instance, while differences in grade and the radius of a circular bend might influence aspects of roadway design, they do not define what superelevation is. Instead, superelevation focuses specifically on the transition of the cross slope to promote a safer and smoother driving experience when navigating curves.