rural and 4,400 are in urban areas. About 15 percent of the mileage as it now exists is already adequate according to the standards established in this study.
These estimates include no allowances for any increase, by the end of 1964, of total mileage in the system. There will, however, be an increase of about 50 percent in traveled lanes. For a substantial portion of the system, nearly 7,000 miles, a 2-lane road will be adequate. The bulk of the proposed improvements, more than 28,000 miles, will be in the 4-lane divided highway category. About 2,300 miles will be 6 or more lanes wide. This latter mileage will, of course, be principally in and approaching the heavier populated areas. Figure 2 shows the approximate location and estimated status of improvement as to lane width, in 1965, of the rural portions of the interstate system.
Construction costs (including structures and right-of-way) on the interstate system range in average from $200,000 a mile for 2-lane roads in rural areas to $10 million a mile for multilane sections (over 6 lanes) in urban areas. ‘There are, of course, wide variations from these averages among the States and for individual road sections. In terms of mileage to be constructed, the 4-lane road predominates. Costs of this 4-lane mileage average $450,000 per mile, rural and $1,600,000 per mile, urban.
Needed work on the interstate system during the 10-year period 1955–64, according to the State estimates, totals $23.2 billion, of which $12.5 billion is in rural and $10.7 billion in urban areas.
This estimate provides for the development of the interstate system in its present designated extent of 37,700 miles. It does not take into account extensions which will undoubtedly be made within the legislative limitation of 40,000 miles—extensions which will in all probability be almost entirely within and adjacent to the larger urban areas. Estimates of the needs for improvement of these extensions must necessarily await their designation. To a certain extent, the needs are contained in the estimates reported for other road systems.
Other Federal-aid systems
About 75 percent of the presently designated Federal-aid primary system (excluding interstate system mileage) will need some kind of improvement during the 10-year period 1955–64. The comparable value for the Federal-aid secondary system is about 68 percent.
At the end of the 10-year period there will be about 201,000 miles of primary system mileage in service, 185,000 miles rural and 16,000 miles urban. The total of 201,000 miles represents an increase over the 193,000 miles in service in 1953, brought about by the inclusion of extensions anticipated by the States.
The Federal-aid secondary system is also expected to grow. On this system, however, the anticipated increase is somewhat larger in proportion, amounting to a 15-percent increase by 1964 over the miles In service in 1953. (On the basis of past rates, an increase of 20 to 25 percent is indicated.) The mileage in service at the end of the 10-year period on this system has been estimated by the States to be about 530,000 miles and is about evenly divided between roads under State control and those under local control.
