In this chart a comparison is made between the 1954 and 1958 estimates of
the cost of completing the Interstate network as originally designated. In
addition, the bar at the right shows 1958 estimate of costs of completing the
total 41,000 mile officially designated Interstate system.
The major reasons for the difference between the 1954 and 1958 Estimates
of cost for completing the officially designated Interstate System are:
1. The 1956 Federal-Aid Highway Act increased the total mileage another
1,000 miles, after the 1954 estimate was prepared. An estimated cost of
constructing this thousand miles has been included as part of the upper
right-hand chart.
2. Highway construction costs increased approximately 12% between 1954
and 1958 estimate periods.
3. The 1975 traffic forecast design basis set forth in the Act of 1956 is approxi-
mately 15% higher than the traffic forecast that was used for the 1954
estimate.
4. Requirements of the Act of 1956 to give equal consideration to local needs
are responsible for over one-third of the total increase. The result is an
increased number of separation structures, interchanges, frontage roads
and extended urban facilities.
5. The 1958 estimate is a sound engineering finding, produced by 1.2 million
man-hours and 12 months of work on the part of the State highway
departments, and was arrived at by applying the official Interstate design
standards and current highway costs to logical highway locations making
up the completion of the Interstate system. This cost estimate is that
required to produce the controlled access type of modern facility authorized
by the Congress.
Although some slight variation can be expected in the subsequent
Interstate estimates which are provided by law, it appears that a point of
substantial stability in estimating the cost of the system has now been
reached. This is based on the fact that the actual cost of current Inter-
state work is running approximately 5% under the 1958 estimate and
present highway costs have stabilized. Of course, inflation or Federal
legislation that would add to Interstate mileage could increase the costs.
These would be items over which the highway departments would have
little or no control.
Based on the 1958 estimate, the current 1960 fiscal year authorization
of $2.5 billion for the Interstate system would have to be continued
annually and without interruption through the 1972 fiscal year to provide
for the completion of the network by 1975-a network designed for the
traffic of 1975.