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FHWA Home / Policy & Governmental Affairs / 2002 Conditions and Performance

Conditions and Performance


Status of the Nation's Highways, Bridges, and Transit:
2002 Conditions and Performance Report

Exhibit 11-37:

Year of Construction and Cumulative ADT - Deficient Timber Superstructure Bridges

Exhibit 11-37

Exhibit 11-37 is a bar graph that shows the year of construction and cumulative ADT for deficient timber superstructure bridges. The vertical axis measures number of bridges from 0 to 4,000 in increments of 500 bridges. The horizontal axis has 21 bars, one for each 5-year period between 1900 and 2000. Each bar has three parts, measuring the distribution of functionally obsolete, structurally deficient, and non-deficient timber bridges. Before 1900, half of the Nation's timber bridges were deficient, with the rest split between non-deficient and obsolete about 2-to-1. From 1900 to 1925, there were fewer than 200 new timber bridges for each 5-year period, most of which were deficient. That trend continued during the periods of greater construction between 1926 to 1950. After 1950, the pattern changed so that half the Nation's new timber bridges were non-deficient, with the rest split between deficient and obsolete about 3-to-1. By 1991, almost all new timber bridges were non-deficient. There are three other items and a second vertical axis (measuring percentages from 0 to 100 in increments of 10 percent) in this chart. A line, representing the "linear" percent of deficient timber bridges for each year of construction by ADT, starts in 1900 at about 90 percent and drops in a straight line to 70 percent by 1935, 50 by 1960, 40 by 1980, and 25 by 2000. A series of small squares, representing the percent of deficient timber bridges for each year of construction by ADT, starts at about 75 percent, climbs to a peak of 90 percent by 1910, drops to 60 in 1915, rises to 85 in 1920, drops to between 60 and 70 between 1921 and 1950, rises to 80 in 1955, and falls to 55 by 1970, 40 by 1985, 10 by 1995, and 0 by 2000. And a series of small triangles, representing the percent of deficient steel bridges for each year of construction by numbers, generally copies the path of the squares, except at between 1 and 10 percentage points lower.
Source: National Bridge Inventory.


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Page last modified on November 7, 2014
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