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Table 4 illustrates the very satisfactory condition regarding vertical clearance. As will be noted, the 133 structures with vertical clearance below the recommended minimum acceptable standard are less than 1 percent of the total number of bridges. The number with clearances less than the 14 feet recommended as desirable for new or reconstructed bridges is considerably less than 5 percent. By showing that less than 10 percent of all bridges have vertical clearances of 17 feet or less, the table indicates the very great extent to which vertical clearance of existing bridges on the network is practically unlimited.

In part, the bridges deficient in vertical clearance are also deficient in horizontal clearance, and those deficient in either or both of these respects are included in part among the 2,436 that are of substandard load capacity. The totals given for each class of deficiency are not additive. The number of different bridges affected is less than 3,000.