an element that has revolutionized
methods of construction and maintenance.

A different set of traffic conditions exists in those parts of the
United States where large areas are devoted primarily to industrial
pursuits, the agricultural development being of secondary importance.
Public highways connecting the industrial centers are indispensable
adjuncts to the business facilities in such communities and are
ordinarily subjected to a very large volume and tonnage of traffic
consisting principally of motor vehicles. The roads first selected for
improvement will not be those serving the agricultural interests of
the district, but rather those serving the industrial centers.
Inter-city roads of great durability and relatively high cost are
necessary for such traffic conditions.

Not infrequently the transportation needs will require a system of
both inter-city and rural highways in the same community. There are
few areas in the United States where there is no agricultural
development. It is apparent therefore that the nature of the highway
systems and the administrative organization under which they are built
and maintained will differ in various states or areas according to
the nature of development of that area agriculturally and
industrially. In planning improvements of highway systems, it is
recognized that one or more of several groups of traffic may be
encountered and that the extent and nature of the improvement must be
such as will meet the requirements of all classes of traffic, the most
important being first provided for, and that of lesser importance as
rapidly as finances permit.

KINDS OF TRAFFIC ON PUBLIC HIGHWAYS

=Local or Farm to Market Traffic.=--In strictly agricultural
communities the principal use of the highways will pertain to
agricultural activities and most of it will be between the farm and
the most convenient market center. In the ordinary state, the number
of rural families will not average more than six to eight per square
mile, but in some districts it may reach twenty families per square
mile. The travel from the district around a market center will
originate in this rather sparsely populated area and converge onto a
few main roads leading to market. The outlying or feeder roads will be
used by only a few families, but the density of traffic will increase
nearer the market centers and consequently the roads nearer town will
be much more heavily traveled than the outlying ones. It is