able. All but 1,625 of these sections are on either two- or three-lane roads. The 1,625 sections on multilane highways total 161 miles in length; the two- and three-lane mileage involved is 1,926.
Safe and satisfactory operation on these sections can, in some cases, be provided by the removal of view obstructions such as trees, cut-slopes, and nearby buildings; but in the great majority the alinement or profile of the road, or both, must be changed to flatten horizontal or vertical curves.
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Safe passing distance and essential capacity
Passing sight distance is required only on two-way roadways of two and three lanes. Of these categories, on the rural system, there are 29,287 miles, including about 11 miles that are unsurfaced; and of this total, passing sight distance is undesirably restricted on 7,324 miles or about 25 percent.