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Summary
Road
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Conditions
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System Conditions
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Bridge Conditions
This section uses two measures of bridge conditions: bridge component
ratings, and the number of deficient bridges. The bridge component ratings
provide a broader perspective on conditions, but the quantity of deficient
bridges is a more widely used indicator. The bridge investment requirement
analysis described later in this report focuses on bridge deficiencies. In
addition, the Federal Highway Administration 1998 National Strategic
Plan includes two goals related to percentage of deficient bridge. The
target for NHS bridges is discussed in Appendix B. The target for all bridges
is discussed later in this chapter.
Bridge Component
Ratings
The National Bridge Inventory (NBI) contains ratings on the conditions of
three major bridge components: deck, superstructure, and substructure. Exhibit
3-18 contains a description of this rating system.
Exhibit 3-18. Bridge
Component Ratings
Exhibit 3-19 illustrates the distribution of bridge component ratings. The
majority of bridge components are rated 7 or higher, indicating that they are
in good, very good, or excellent condition. Approximately one-third are rated 5
or 6, indicating that they are considered fair or satisfactory. The remainder
of bridge components are rated 4 or lower, indicating that they are in poor or
worse condition. A component rating does not translate directly into an overall
rating of a bridge's condition.
Exhibit 3-19. Bridge
Component Conditions, 1998
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