In contrast, deficiencies of least degree are found on 12,778 miles, all of which are improved with pavements at least 20 feet wide and in no case more than 2 feet narrower than the standard width prescribed for the volume of traffic served.
To raise the entire rural network to the standards of pavement width prescribed, table 7 shows that it will be necessary to widen existing pavements as follows:
To 20-foot width:
- 2,004 miles now less than 18 feet wide.
- 5,357 miles now 18 but less than 20 feet wide.
To 22-foot width:
- 2,049 miles now less than 18 feet wide.
- 12,673 miles now 18 but less than 20 feet wide.
- 11,671 miles now 20 but less thap 22 feet wide.
To 24-foot width:
- 1,037 miles now less than 18 feet wide.
- 6,559 miles now 18 but less than 20 feet wide.
- 5,753 miles now 20 but less than 22 feet wide.
- 1,107 miles now 22 but less than 24 feet wide.
The strength of existing road surfaces approaches the desirable standard more nearly than their width. It has not been possible to determine with great accuracy the strength of all surfaces; but the facts available regarding their general type indicate that not more than about 14,000 miles of the rural network are incapable of supporting 9,000-pound wheel loads on pneumatic tires the year round. In very large part the surfaces deficient in strength arc also deficient in width and other qualities.
Excessive curvature and inadequate sight distances are among the more common defects of existing improvements. Perhaps the most common defect is a general lack of shoulders of sufficient width to accommodate standing vehicles. The construction of narrow shoulders has been considered in the past a permissible cost-saving expedient. As a result there are few roads today where the space between the pavement and ditch or edge of fill is sufficient to insure the safety of parked vehicles and the traffic moving by them.
Entirely apart from considerations of defense usage, adequate provision for normal civil traffic on the more heavily traveled routes will require in the future a rather general widening of existing shoulders. But the possibility of more or less frequent use of a substantial part of the strategic network by motorized and mechanized Army convoys adds another important reason for building wider shoulders.
As a practical approach to this generally desirable condition, many of the State Highway departments have indicated a preference for constructing wider shoulders at staggered intervals on the two sides of the road. But even so, the sections of the rural network on which they report immediate shoulder widening to be desirable, aggregate more than 42,700 miles.
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P-7103
