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Rh one at which the selected route would pass over, the intersecting road. On the above bases of length and width, estimates were made for the following classes of structures at the costs assigned to each:

For stream bridges, less than 100 feet in length, $10 per square foot. For long stream bridges the estimates varied in accordance with conditions found at the sites. Costs ranged from $6.50 to $28.50 per square foot.

For bridges over railroads $15 per square foot plus $10,000 and for railroad bridges $20 per square foot plus $10,000.

For highway separation bridges in rural areas $15 per square foot plus $10,000, and in urban areas $17 per square foot plus $16,000.

Cattle passes, or equivalent land purchases, were estimated at about $8,000 for each two-lane and $15,000 for each four-lane highway crossing.

Costs of tunnels were estimated individually in accordance with the geological formation encountered.

Three general types of accesses were estimated at the following lump sums:

(A) Accesses to two-lane roads widened to three lanes at the intersection, with two toll booths, at a lump sum of $70,000 for each point of access. This lump sum included:

Grading, paving, and appurtenances of the accesses.

Widening to a three-lane highway for about 2,000 feet.

Transitions for the approaches to the widened portion.

Additional width of grade-separation structure.

(B) Accesses to two-lane roads widened to four lanes divided at the intersection, with two toll booths, at a lump sum of $240,000 for each point of access. The items involved are the same as for type A except that the item of widening involves a four-lane divided highway for about 3,700 feet.

(C) Accesses to four-lane roads, with two or more toll booths, at a lump sum of $50,000 for each point of access. The items involved are the same as for type A except those due to the widening of the selected route.

Type A was used for all two-lane sections except those which are expected to carry near-capacity traffic, where widening to a four-lane divided highway may reasonably be expected in a comparatively short time, in which case type B was used.

The field form used for estimating costs is illustrated by the typical sheets shown in plates 46 and 47. Estimates prepared on these forms were summarized by access points, by counties, by sections, and by routes.

The total cost for right-of-way and construction of the 14,336.2 miles of the selected routes, as estimated in the manner above described, including 10 percent for engineering, contingencies, and interest during construction, is $2,899,770,145, which is at the average rate of $202,270 per mile. The average costs estimated vary from a maximum of $1,158,412 per mile for the 65.6-mile section from Jersey City, N. J., to New Haven, Conn., to a minimum of $63,450 per mile for the 119.7-mile section from Rupert, Idaho, to Brigham, Utah.

Table 4 gives a summary of the physical features involved and the estimated costs by routes.

Tables 5 to 15 show a distribution of construction costs by items for the system and for each route, subdivided by States.