Sight distance is a safety design factor which is intrinsically linked to rate of change of grade, and hence
to K-values.
Consider once again the hump-backed bridge. Drivers approaching from each side of this particular
vertical curve cannot see each other until they arrive, simultaneously, almost on the crest; by which time it
may be too late to prevent an accident. Had the curve been longer and flatter, thus resulting in a low rate of
change of grade, the drivers would have had a longer sight distance and consequently more time in which
to take avoiding action.
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