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

Year of Construction and Cumulative ADT - All Structures

Exhibit 11-7 is a bar graph that shows the year of construction and cumulative ADT for all structures. The vertical axis measures number of bridges from 0 to 60,000 in increments of 10,000 bridges. The horizontal axis has 21 bars, one for each 5-year period between 1900 and 2000. The first bar shows that 10,000 bridges were built before 1900. From 1901 to 1925, construction rose from about 2,000 to 10,000. From 1926 to 1940, construction rose rapidly from 22,000 to 32,000. Construction dropped during WWII then rebounded to pre-war levels in the late 1940s and early 1950s. The peak years for construction were between 1956 and 1970, when between 52,000 and 55,000 bridges were built in each of the three 5-year periods. Construction has dropped steadily since then, to more than 40,000 in 1971-75 and 1986-90; less than 40,000 in 1976-80 and 1981-85; 40,000 in 1991-1995; and 33,000 in 1996-2000. There are also two lines on the graph; the vertical axis on the right of the chart measures percentages from 0 to 100 in increments of 10 percent. The first line, for cumulative percent of structure population, is just above 0 from 1900 to 1920, rises to 20 percent by 1940, 40 percent by 1960, 60 percent by 1970, 82 percent by 1990, and 100 percent in 2000. The other line, for cumulative percent of ADT, is just above 0 from 1900 to 1925, rises to 20 percent by 1955, 30 percent by 1960, 70 percent by 1970, 90 percent by 1990, and 100 percent in 2000.

Source: National Bridge Inventory.

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