Page:America's Highways 1776–1976.djvu/421



The mileage record of the concrete type differs considerably from the other types. For the rural mileage during the 1920’s and early 1930’s, the total exceeded that of both bituminous types. The existing rural concrete pavement mileage increased until 1935, leveled off for some 10 years, and since has decreased.

The mileage decrease for rural concrete pavements reflects the conversion of sections of that type of pavement to the high bituminous type when an overlay was placed as a maintenance step. The existing urban concrete mileage for the last 16 years shows no increase, the mileage being only half or less those of bituminous pavements. The overlay conversion effect doubtless applies here also.

Proportionally, there has been substantially higher type development of road and street mileage in the urban area. The percentages of the 1973 mileages for the various types were: