Page:Highway Needs of the National Defense.pdf/58

42 Of the 7,324 miles, 3,968 miles carried an hourly traffic of less than 500 vehicles in 1948. Roads that carried traffic in excess of 800 vehicles hourly aggregate 1,456 miles. The remainder, 1,900 miles, is on roads that carried traffic of between 500 and 800 vehicles an hour.

Correction of deficiencies

Correction of these passing-sight-distance deficiencies can be accomplished in three ways, as follows:


 * 1) By improving the alinement and profile of the existing highway. This may involve the relocation of short sections where horizontal curves cause the restriction; or it may necessitate additional excavation at the summit of grades where the restriction is caused by short vertical curvature.
 * 2) By constructing another highway that will meet the required standards on a new location.
 * 3) By constructing an additional two-lane highway, which with the existing highway will form a divided four-lane highway, on which sight distance of the extent required for safe passing on two- and three-lane roads is not needed.

Of these three means the choice of the most feasible depends on such conditions as the relative adequacy of the surface and other features of the existing road and the present and estimated future traffic.

Conversion to four-lane divided highways

The expenditure of any substantial sum for the lengthening of sight distance on the 1,456 miles that carried hourly traffic of 800 vehicles or more will be wasteful. These roads should be promptly transformed into four-lane divided highways.

Correction of sight-distance deficiencies on the 1,900 miles carrying 500 to 800 vehicles hourly will generally require extensive relocation to develop the alinement needed to provide the sight distance necessary for these roads as two- and three-lane highways. The traffic on these roads is increasing, and in the not distant future may be expected to reach volumes requiring the capacity of divided four-lane highways. When this is done the extended sight distance will not be required. For this reason, the more feasible and perhaps less costly correction in the case of a high percentage of the roads carrying between 500 and 800 vehicles hourly would appear to be early replacement of the existing two- and three-lane roads with four lanes, divided.

Likewise, it may be more feasible to reconstruct to four lanes some of the 3,968 miles now carrying less than 500 vehicles per hour, especially those sections in rough terrain where extensive work would be required to lengthen the sight distance to the required standards.

DEFICIENCY OF INTERSECTION WITH RAILROADS

The defined standards require elimination of all grade crossings of railroads consisting of two or more main-line tracks, and of all crossings of single-track lines on which there are six or more train movements daily.

The 218 remaining crossings of the first category and 542 of the second, a total of 760 crossings, are definitely of sufficient hazard to warrant their elimination.

The need for elimination of the remaining 502 grade crossings of single main-line tracks carrying less than six daily train movements and