When it comes to descending, visibility is extremely important as it helps one to prepare for what is ahead. If visibility is bad, it may be difficult to spot parked cars, debris, or other changes on the road surface. Never exceeding a speed at which you can absolutely see, removes any surprises and lets you choose the quickest and safest way around corners. Last but not the least; tree lines or road signs can also be used when the exit of a corner radius is not visible to estimate how much the corner gets sharper.