When designing a hill in a road, what special number helps figure out how long the curve should be for safe sight?

When designing a hill in a road, the special number that helps determine how long the curve should be for safe sight is called the K-value. The K-value represents the horizontal length of the vertical curve required for each one percent of algebraic difference in grade. A vertical curve is a parabolic arc used to smoothly connect two intersecting road grades, which are the slopes of the road, typically expressed as percentages. For example, a +3% uphill grade ....