Deficiencies of both pavement and shoulder width
Approximately half of the rural mileage of the system is deficient in both shoulder and surface width. On this mileage, surfaces already too narrow are further constricted whenever a vehicle has to stop for any reason along the way.
Of the entire rural mileage, 5,500 miles at most are adequate in both surface and shoulder width.
Urban width deficiencies
Streets in urban areas should have greater paved widths than rural roads because of the general absence of shoulders and greater frequency of parking. It is, therefore, a startling commentary upon the width of the urban interstate system mileage to find that 2,391 of the 4,141 urban miles for which complete data are available are inadequate in paved width even by the rural road standard.
DEFICIENCY OF CURVATURE
On rural sections of the system there are 3,199 curves of more than 14 degrees, the maximum recognized by the standards as permissible in mountainous areas, and more than half of them are in areas classed as flat or rolling.
There are 15,115 curves, or approximately one every 2 miles on the average, that are sharper than the standard specified as desirable for the type of terrain in which they are located. Of those, 11,182 are sharper than the maximum prescribed by the standards for the desirable design speed; and 6,473 are sharper than the maximum per-
92989—49-——4
