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

Chapter 3: System Conditions
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Index
Introduction
Highlights
Executive Summary
Part I: Description of Current System
Ch1: The Role of Highways and Transit
Ch2: System and Use Characteristics
Ch3: System Conditions
Ch4: Operational Performance
Ch5: Safety Performance
Ch6: Finance

Part II: Investment Performance Analyses
Ch7: Capital Investment Requirements
Ch8: Comparison of Spending and Investment Requirements
Ch9: Impacts of Investment
Ch10: Sensitivity Analysis

Part III: Bridges
Ch11: Federal Bridge Program Status of the Nation's Bridges

Part IV: Special Topics
Ch12: National Security
Ch13: Highway Transportation in Society
Ch14: The Importance of Public Transportation
Ch15: Macroeconomic Benefits of Highway Investment
Ch16: Pricing
Ch17: Transportation Asset Management
Ch18: Travel Model Improvement Program
Ch19: Air Quality
Ch20: Federal Safety Initiatives
Ch21: Operations Strategies
Ch22: Freight

Part V: Supplemental Analyses of System Components
Ch23: Interstate System
Ch24: National Highway System
Ch25: NHS Freight Connectors
Ch26: Highway-Rail Grade Crossings
Ch27: Transit Systems on Federal Lands

Appendices
Appendix A: Changes in Highway Investment Requirements Methodology
Appendix B: Bridge Investment/Performance Methodology
Appendix C: Transit Investment Condition and Investment Requirements Methodology
List of Contacts

Bridge Conditions

Three indicators are examined in this section: bridge condition ratings, the number of deficient bridges, and the percentage of deck area on deficient bridges. Each measure examines bridge conditions from a different perspective. Condition ratings provide a numerical evaluation of the condition of a bridge element. The number of deficient bridges is widely used by policymakers to describe bridge conditions nationwide, but it does not recognize the relative importance, from a mobility perspective, of an individual bridgeís contribution to the overall transportation system. The final indicatoróthe percentage of deck area on bridges classified as deficientóis increasingly used to document the state of bridge conditions; for example, the FY 2002 FHWA Performance Plan includes this measure as its new indicator. This chapter describes deck area on deficient bridges by owner and functional system. Information on National Highway System (NHS) bridges is described in Chapter 24.

Bridge Condition Ratings

The National Bridge Inventory (NBI) contains ratings on the conditions of three major bridge components: the deck, superstructure, and substructure. A bridge deck is the primary surface used for transportation. The deck is supported by the superstructure, which carries the load of the deck and the traffic. Within the superstructure are the girders, stringers, and other structural elements. The substructure is the foundation of the bridge and transfers the loads of the structure to the ground. The superstructure is supported by substructure elements, such as abutments and piers. Exhibit 3-21 describes bridge condition ratings in greater detail.

    
Exhibit 3-21

Bridge Condition Ratings
RATING
CATEGORY
DESCRIPTION
9
Excellent Condition  
8
Very Good Condition  
7
Good Condition No problems noted.
6
Satisfactory Condition Some minor problems.
5
Fair Condition All primary structural elements are sound but may have minor section loss, cracking, spalling, or scour.
4
Poor Condition Advanced section loss, deterioration, spalling or scour.
3
Serious Condition Loss of section, deterioration, spalling or scour have seriously affected primary structural components. Local failures are possible. Fatigue cracks in steel or shear cracks in concrete may be present.
2
Critical Condition Advanced deterioration of primary structural elements. Fatigue cracks in steel or shear cracks in concrete may be present or scour may have removed substructure support. Unless closely monitored, it may be necessary to close the bridge until corrective action is taken.
1
Imminent Failure Condition Major deterioration or section loss present in critical structural components, or obvious loss present in critical structural components, or obvious vertical or horizontal movement affecting structure stability. Bridge is closed to traffic but corrective action may put back in light service.
0
Failed Condition Out of service; beyond corrective action.
Source: "Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation's Bridges," December 1995.

Condition ratings are used to describe the existing, inplace status of a component, not its as-built state. Engineers assign condition ratings by evaluating the severity of deterioration or disrepair and the extent to which it is widespread throughout the component being rated. A condition rating does not translate directly into an overall rating of a bridgeís condition, but it is a good indicator of the quality of specific elements.

Exhibit 3-22 illustrates the distribution of bridge condition ratings. Most bridge components are rated 7 or higher, indicating that they are in good, very good, or excellent condition. Another one-third of all bridge components are rated 5 or 6, indicating fair or satisfactory condition. The remainder of bridge components are rated 4 or lower, indicating a poor or worse condition.

Bridge Condition Conditions
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Number of Deficient Bridges

The most commonly-cited indicator of bridge condition is the number of deficient bridges. There are two types of deficient bridges: structurally deficient and functionally obsolete. Bridges are considered structurally deficient if they are restricted to light vehicles, require immediate rehabilitation to remain open, or are closed. A deficient bridge may or may not be dangerous, but it does require significant maintenance, rehabilitation, or sometimes replacement. Bridges are considered functionally obsolete if they have deck geometry, load carrying capacity, clearance, or approach roadway alignment that no longer meets the criteria for the system of which the bridge is a part.

Q.
When might a bridge be classified as functionally obsolete?
A.
A bridge can become functionally obsolete because of highway improvements on the approaches to the bridge, such as lane additions or the widening of approaching roads. In other cases, a bridge may be classified as functionally obsolete through a redefinition of desired standards.

As shown by Exhibit 3-23, about 28.5 percent of the Nationís bridges were deficient in 2000. Of these deficient bridges, about 14.8 percent were structurally deficient and 13.8 percent were functionally obsolete.

Deficiencies for All Bridges, 2000
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The number of deficient bridges has steadily decreased over the past decade. In 1994, about 32.5 percent of the Nationís bridges were deficient, but that number had dropped by almost 4 percent by 2000. The long-term trend is consistent with expectations in the Federal Highway Administrationís 1998 Strategic Plan, which stated that less than 25 percent of the Nationís bridges should be deficient by 2008. Exhibit 3-24 describes the trend data in more detail.

Percentage of Deficient Bridges, 1994-2000
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A more specific way of looking at the number of deficient bridges is by owner. As Chapter 2 explained, ownership of bridges is largely divided among State and local governments (47.2 and 50.9 percent, respectively). The remaining bridges, totaling 1.4 percent, are split among the Federal Government, private companies, and entities for which ownership is unknown or not coded in the National Bridge Inventory.

Exhibit 3-25 examines bridge deficiencies by owner. This exhibit shows substantial differences by level of government and type of owner. The Federal Government, for example, has the smallest percentage of deficient bridges (24.8 percent), but also owns a relatively small number of bridges (8,221). States have almost the same percentage of deficient bridges (24.9 percent), but have a much larger number of bridges (277,106). About 31.8 percent of the 298,889 bridges owned by local governments are deficient, while 53.1 percent of the Nationís 2,299 private bridges are deficientóthe highest percentage of any owner type.

Bridges: Percent Deficient by Ownership, 2000
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Bridges: Percent Deficient by Ownership, 2000
 
FEDERAL STATE LOCAL PRIVATE UNKNOWN TOTAL
Total Bridges
8,221 277,106 298,889 2,299 415 586,930
Total Deficient
2,038 68,832 95,291 1,220 185 167,566
Structurally Deficient
642 25,142 60,196 644 88 86,712
Functionally Obsolete
1,396 43,690 35,095 576 97 80,854
FEDERAL STATE LOCAL PRIVATE UNKNOWN TOTAL
Percent Deficient
24.80% 24.80% 31.90% 53.10% 44.60% 28.50%
Percent Structurally Deficient
7.80% 9.10% 20.10% 28.00% 21.20% 14.80%
Percent Functionally Obsolete
17.00% 15.80% 11.70% 25.10% 23.40% 13.80%
Total Deficient
24.80% 24.90% 31.80% 53.10% 44.60% 28.60%
Source: National Bridge Inventory.

Most deficiencies on locally-owned bridges are structural, while most deficiencies on State and Federal bridges involve functional obsolescence. Exhibits 3-26 and 3-27 illustrate this phenomenon. About 69.5 percent of structurally deficient bridges were locally-owned, 29 percent were State-owned, and the remaining 1.5 percent were owned by the Federal Government, private companies, or other entities. Conversely, States owned about 54 percent of all functionally obsolete bridges. Local governments owned 43.4 percent of functionally obsolete bridges, and Federal, private, and other entities owned the remaining 2.6 percent.

Ownership of Structurally Deficient Bridges, 2000
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Ownership of Functionally Obsolete Bridges, 2000
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Another way of looking at the number of deficient bridges is by rural and urban location. As Chapter 2 noted, 77.5 percent of bridges were in rural communities in 2000. About 27.6 percent of these rural bridges were deficient. At the same time, about 31.9 percent of the nationís urban bridges were deficient; therefore, urban bridges are more likely to be deficient than their rural counterparts.

Bridge condition in both urban and rural areas has steadily improved over the past decade. Exhibit 3-28 shows that the number of deficient rural bridges dropped from 31.8 percent in 1994 to 27.6 percent in 2000. More specifically, the number of structurally deficient rural bridges dropped from 20.2 percent in 1994 to 16.2 percent in 2000. The number of functionally obsolete rural bridges decreased less dramaticallyófrom 11.6 percent in 1994 to 11.4 percent in 2000.

Exhibit 3-28 also shows that the number of deficient urban bridges dropped from 35.3 percent in 1994 to 31.9 percent in 2000. The number of structurally deficient urban bridges decreased from 13 percent in 1994 to 9.9 percent in 2000, while the number of functionally obsolete bridges diminished only slightly, from 22.3 percent in 1994 to 22 percent in 2000. The significant drop in urban bridge deficiency, therefore, can largely be attributed to improvements in the structural integrity of bridges in metropolitan areas.

Rural and Urban Bridge Deficiencies, 1994-2000
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Rural and Urban Bridge Deficiencies, 1994-2000
 
  1994 1996 1998 2000
NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT
Rural Bridges
455,319
456,913
454,664
455,365
Deficient Bridges
144,799
31.8%
139,545
30.5%
130,911
28.8%
125,523
27.6%
Structurally Deficient
91,991
20.2%
86,424
18.9%
78,999
17.4%
73,599
16.2%
Functionally Obsolete
52,808
11.6%
53,121
11.6%
51,912
11.4%
51,924
11.4%
Urban Bridges
121,141
124,949
128,312
131,781
Deficient Bridges
42,716
35.3%
43,181
34.6%
41,661
32.5%
42,031
31.9%
Structurally Deficient
15,692
13.0%
15,094
12.1%
14,073
11.0%
13,079
9.9%
Functionally Obsolete
27,024
22.3%
28,087
22.5%
27,558
21.5%
28,952
22.0%
Total Bridges
576,460
581,862
582,976
587,146
Deficient Bridges
187,515
32.5%
182,726
31.4%
172,572
29.6%
167,554
28.5%
Structurally Deficient
107,683
18.7%
101,518
17.4%
93,072
16.0%
86,678
14.8%
Functionally Obsolete
79,832
13.8%
81,208
14.0%
79,500
13.6%
80,876
13.8%
Source: National Bridge Inventory.

Exhibit 3-29 elaborates on a central conclusion of the previous section: that bridges are more likely to be deficient in urban areas. Bridges on urban Interstates, urban principal arterials, and urban minor arterials have a higher percentage of deficiencies than those on comparable rural functional systems. Local functional class bridges represent a break from this pattern. A larger percentage of rural local functional class bridges are deficient (34.7 percent) than urban local functional class bridges (31.6 percent).

Bridges: Percent Deficient by Functional System, 2000
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Bridges: Percent Deficient by Functional System, 2000
 
  TOTAL BRIDGES BRIDGE DEFICIENCIES PERCENT DEFICIENT
STRUCTURAL FUNCTIONAL TOTAL STRUCTURAL FUNCTIONAL TOTAL
FUNCTIONAL CLASS
Rural
Interstate
27,797
1,076
3,384
4,460
3.90%
12.20%
16.00%
Other Principal Arterial
35,419
1,946
3,642
5,588
5.50%
10.30%
15.80%
Minor Arterial
39,377
3,509
4,551
8,060
8.90%
11.60%
20.50%
Major Collector
95,559
11,839
10,258
22,097
12.40%
10.70%
23.10%
Minor Collector
47,798
7,118
5,567
12,685
14.90%
11.60%
26.50%
Local
209,415
48,111
24,522
72,633
23.00%
11.70%
34.70%
Total Rural
455,365
73,599
51,924
125,523
16.20%
11.40%
27.60%
Urban
Interstate
27,882
1,809
5,727
7,536
6.50%
20.50%
27.00%
Other Freeway and Expressway
16,011
1,000
3,358
4,358
6.20%
21.00%
27.20%
Other Principal Arterial
24,146
2,439
5,396
7,835
10.10%
22.30%
32.40%
Minor Arterial
23,020
2,574
6,002
8,576
11.20%
26.10%
37.30%
Collector
15,038
1,908
3,707
5,615
12.70%
24.70%
37.30%
Local
25,684
3,349
4,762
8,111
13.00%
18.50%
31.60%
Total Urban
131,781
13,079
28,952
42,031
9.90%
22.00%
31.90%
Total, Rural and Urban
587,146
86,678
80,876
167,554
14.80%
13.80%
28.50%
Source: National Bridge Inventory.

The proportion of structurally deficient and functionally obsolete bridges varies by functional system. Generally, the percentage of bridges that are deficient is greater on lower functional systems. Interstate bridges, for example, have the lowest percentage of deficient bridges (16 percent in rural areas and 27 percent in urban areas). Urban minor arterials and urban collectors have the highest percentage of deficient bridges (37.3 percent for each system). The healthy condition of many higher-level bridges is striking, particularly since these account for a large share of VMT.

Exhibits 3-30 through 3-33 provide a historical perspective on the level of bridge deficiency by functional classification. Generally, bridge condition has improved on Interstates, other principal arterials, collectors, and local roads over the past decade. The greatest decline in deficiency occurred in the early to mid-1990s, particularly for Interstate bridges. Looking more specifically at the types of deficiency, structural deficiency consistently decreased on the systems profiled in Exhibits 3-30 through 3-33, while functional obsolescence either remained relatively constant or even increased slightly. On collectors, for instance, 16.1 percent of bridges were structurally deficient in 1994, but that number had dropped to 13.2 percent by 2000. At the same time, 11.9 percent of collector bridges were functionally obsolete in 1994, but that number had risen to 12.3 percent by 2000.

Interstate Bridge Deficiencies, 1994-2000
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Interstate Bridge Deficiencies, 1994-2000
 
  1994 1996 1998 2000
NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT
Rural Bridges
28,865
 
28,683
 
27,530
 
27,797
 
Deficient Bridges
5,342
18.5%
5,479
19.1%
4,504
16.4%
4,460
16.0%
Structurally Deficient
1,162
4.0%
1,249
4.4%
1,135
4.1%
1,076
3.9%
Functionally Obsolete
4,180
14.5%
4,230
14.7%
3,369
12.2%
3,384
12.2%
Urban Bridges
25,861
 
26,596
 
27,480
 
27,882
 
Deficient Bridges
7,920
30.6%
8,181
30.8%
7,376
26.8%
7,536
27.0%
Structurally Deficient
2,141
8.3%
2,070
7.8%
1,850
6.7%
1,809
6.5%
Functionally Obsolete
5,779
22.3%
6,111
23.0%
5,526
20.1%
5,727
20.5%
Total Bridges
54,726
 
55,234
 
55,010
 
55,679
 
Deficient Bridges
13,262
24.2%
13,660
24.7%
11,880
21.6%
11,996
21.5%
Structurally Deficient
3,303
6.0%
3,319
6.0%
2,985
5.4%
2,885
5.2%
Functionally Obsolete
9,959
18.2%
10,341
18.7%
8,895
16.2%
9,111
16.4%
Source: National Bridge Inventory.
Other Arterial Bridge Deficiencies, 1994-2000
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Other Arterial Bridge Deficiencies, 1994-2000
 
  1994 1996 1998 2000
NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT
Rural Bridges
72,453   72,970   73,324   74,796  
Deficient Bridges
15,693 21.7% 15,693 21.5% 14,216 19.4% 13,648 18.2%
Structurally Deficient
6,914 9.5% 6,622 9.1% 6,060 8.3% 5,455 7.3%
Functionally Obsolete
8,779 12.1% 9,071 12.4% 8,156 11.1% 8,193 11.0%
Urban Bridges
57,012   59,064   60,901   63,177  
Deficient Bridges
20,506 36.0% 20,710 35.1% 20,435 33.6% 20,769 32.9%
Structurally Deficient
7,247 12.7% 6,902 11.7% 6,467 10.6% 6,013 9.5%
Functionally Obsolete
13,259 23.3% 13,808 23.4% 13,968 22.9% 14,756 23.4%
Total Bridges
129,465   132,034   134,225   137,973  
Deficient Bridges
36,199 28.0% 36,403 27.6% 34,651 25.8% 34,417 24.9%
Structurally Deficient
14,161 10.9% 13,524 10.2% 12,527 9.3% 11,468 8.3%
Functionally Obsolete
22,038 17.0% 22,879 17.3% 22,124 16.5% 22,949 16.6%
Source: National Bridge Inventory.

Q.
Why has the percentage of functionally obsolete bridges not dropped in a similar manner as the percentage of structurally deficient bridges?
A.
One reason may be the worsening performance of many systems. Since functional obsolescence indicates that a bridge cannot meet the capacity of the road it serves, increasing congestion would likely make many bridges functionally obsolete.
Collector Bridge Deficiencies, 1994-2000
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Collector Bridge Deficiencies, 1994-2000
 
1994 1996 1998 2000
TOTAL BRIDGES
NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT
Rural Bridges
147,612   144,246   143,140   143,357  
Deficient Bridges
39,398 26.7% 37,158 25.8% 35,368 24.7% 34,782 24.3%
Structurally Deficient
23,645 16.0% 21,375 14.8% 19,919 13.9% 18,957 13.2%
Functionally Obsolete
15,753 10.7% 15,783 10.9% 15,449 10.8% 15,825 11.0%
Urban Bridges
14,702   14,848   14,962   15,038  
Deficient Bridges
5,932 40.3% 5,976 40.2% 5,718 38.2% 5,615 37.3%
Structurally Deficient
2,415 16.4% 2,337 15.7% 2,158 14.4% 1,908 12.7%
Functionally Obsolete
3,517 23.9% 3,639 24.5% 3,560 23.8% 3,707 24.7%
Total Bridges
162,314   159,094   158,102   158,395  
Deficient Bridges
45,330 27.9% 43,134 27.1% 41,086 26.0% 40,397 25.5%
Structurally Deficient
26,060 16.1% 23,712 14.9% 22,077 14.0% 20,865 13.2%
Functionally Obsolete
19,270 11.9% 19,422 12.2% 19,009 12.0% 19,532 12.3%
Source: National Bridge Inventory.

Local Bridge Deficiencies, 1994-2000
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Local Bridge Deficiencies, 1994-2000
 
  1994 1996 1998 2000
TOTAL BRIDGES
NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT NUMBER PERCENT
Rural Bridges
206,389 211,059 210,670 209,415
Deficient Bridges
84,366 40.9% 81,215 38.5% 76,823 36.5% 72,633 34.7%
Structurally Deficient
60,270 29.2% 57,178 27.1% 51,885 24.6% 48,111 23.0%
Functionally Obsolete
24,096 11.7% 24,037 11.4% 24,938 11.8% 24,522 11.7%
Urban Bridges
23,566 24,441 24,969 25,684
Deficient Bridges
8,358 35.5% 8,314 34.0% 8,132 32.6% 8,111 31.6%
Structurally Deficient
3,889 16.5% 3,785 15.5% 3,598 14.4% 3,349 13.0%
Functionally Obsolete
4,469 19.0% 4,529 18.5% 4,534 18.2% 4,762 18.5%
Total Bridges
229,955 235,500 235,639 235,099
Deficient Bridges
92,724 40.3% 89,529 38.0% 84,955 36.1% 80,744 34.3%
Structurally Deficient
64,159 27.9% 60,963 25.9% 55,483 23.5% 51,460 21.9%
Functionally Obsolete
28,565 12.4% 28,566 12.1% 29,472 12.5% 29,284 12.5%
Source: National Bridge Inventory.

Deck Area on Deficient Bridges

A third indicator of bridge condition is deck area on deficient bridges. Engineers and policy analysts are increasingly using this measure to describe the condition of the Nationís bridges. The Federal Highway Administrationís FY 2002 Performance Plan, for example, includes this indicator for NHS and non-NHS bridges. This section examines the deck area on deficient bridges by owner and functional system.

As Exhibit 3-34 describes, the nationwide percentage of deck area on deficient bridges dropped from 30.9 percent in 1996 to 27.9 percent in 2000. Bridges with unknown or unclassified ownership had the largest percentage of deck area on deficient bridges (42.8 percent in 2000), followed by privately owned bridges (33.8 percent). Federally owned bridges had the smallest percentage of deck area on deficient bridges (25.8 percent in 2000).

    
Exhibit 3-34

Deficient Bridge Deck Area by Owner, 1996, 1998, and 2000
 
  Percentage of Deck Area
FUNCTIONAL SYSTEM
1996 1998 2000
Federal
23.8% 26.4% 25.8%
State
29.4% 26.7% 26.4%
Local
35.2% 34.1% 32.8%
Private
38.1% 35.5% 33.8%
Unknown
49.0% 46.3% 42.8%
Total
30.9% 28.5% 27.9%
Source: National Bridge Inventory.

Exhibit 3-35, describes this information by functional system. The percentage of deck area on bridges classified as deficient decreased on every functional system from 1996 to 2000. Urban Collector bridges had the largest percentage (39.6 percent). Using this indicator, the deck area on bridges classified as deficient was consistently larger for urban systems.

    
Exhibit 3-35

Deck Area on Deficient Bridges by Functional System, 1996, 1998, and 2000
 
  Percentage of Deck Area
FUNCTIONAL SYSTEM
1996 1998 2000
Rural
Interstate
17.9% 15.7% 15.0%
Other Principal Arterial
21.6% 19.0% 17.6%
Minor Arterial
26.1% 23.9% 22.9%
Major Collector
23.9% 22.9% 22.7%
Minor Collector
24.7% 23.2% 22.5%
Local
32.3% 30.3% 29.1%
Subtotal
24.6% 22.7% 21.8%
Urban
Interstate
34.2% 30.9% 31.6%
Other Freeway and Expressway
32.4% 28.6% 28.9%
Other Principal Arterial
40.9% 38.3% 36.4%
Minor Arterial
40.3% 39.3% 37.3%
Collector
41.6% 39.3% 39.6%
Local
38.5% 36.7% 36.4%
Subtotal
36.8% 34.0% 33.6%
Bridge Total
30.9% 28.5% 27.9%
Source: National Bridge Inventory.

Exhibit 3-36 describes the percentage of deck area on deficient bridges in 2000, with data broken down by structural deficiency and functional obsolescence. On almost every functional system, the percentage of deck area on functionally obsolete bridges was far greater than the area for structurally deficient bridges. On urban Interstates, for example, 22.8 percent of the deck area on deficient bridges resulted from functionally obsolete bridges while 8.8 percent can be attributed to those bridges classified as structurally deficient.

Deficient Bridge Deck Area by Functional Area, 2000
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Deficient Bridge Deck Area by Functional Area, 2000
 
  Percentage of Deck Area
STRUCTURAL FUNCTIONAL TOTAL
Rural
Interstate
4.5%
10.5%
15.0%
Other Principal Arterial
6.7%
11.0%
17.7%
Minor Arterial
9.7%
13.1%
22.8%
Major Collector
11.8%
11.0%
22.8%
Minor Collector
11.7%
10.8%
22.5%
Local
16.0%
13.0%
29.0%
Total Rural
10.2%
11.6%
21.8%
Urban
Interstate
8.8%
22.8%
31.6%
Other Freeway and Expressway
8.2%
20.7%
28.9%
Other Principal Arterial
13.3%
23.1%
36.4%
Minor Arterial
11.9%
25.4%
37.3%
Collector
13.3%
26.4%
39.7%
Local
11.0%
25.5%
36.5%
Total Urban
10.5%
23.2%
33.7%
Total, Rural and Urban
10.3%
17.6%
27.9%
Source: National Bridge Inventory.
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