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52 routes. In some cases a desirable improvement of the system will doubtless follow locations selected outside of these cities, thus decreasing to some extent the total mileage within municipal limits, but possibly tending to increase slightly the total reported mileage of the system.

The 33,920-mile total mileage reported does not include any allowance for alternate circumferential or distributing routes required at the larger cities for the dual purpose of bypassing through traffic and of distributing and assembling other traffic to and from the several quarters of the city. Although generally a relatively small part of the total, through traffic when joined with the traffic originating in or destined to outlying sections of a city results in a movement so large as to require circumferential routes in addition to direct city-entering connections. These circumferential routes, an essential part of the interregional system, are discussed in some detail in a subsequent section of this report. Since their proper location and mileage can be determined only by detailed study of the needs and conditions of each city involved, the Committee has merely estimated that the aggregate extent of such desirable alternate and auxiliary routes will not exceed 5,000 miles. If added to the more definitely determined mileage of primary routes, this estimated mileage, probably located partly within and partly without municipal limits, would increase the total extent of the recommended system to about 39,000 miles.