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Status of the Nation's Highways, Bridges, and Transit:
2004 Conditions and Performance
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Chapter 2 (Continued)

Bridge System Characteristics

Bridges by Owner

Exhibit 2-13 shows the number of highway bridges by owner from 1996 to 2002. State and local ownership includes highway agencies; park, forest, and reservation agencies; toll authorities; and other State or local agencies, respectively. The vast majority of State and local bridges are owned by highway agencies. Federal ownership includes a number of agencies, mostly from the Department of Interior and the Department of Defense. A small number (less than 1 percent) of bridges carrying public roadways are owned by other agencies, such as private entities and railroads. Ownership percentages have remained relatively constant over time, as shown in Exhibit 2-13.

Q. Is information on railroad bridge inspections included in the NBI?
A.

Some bridges carrying highway traffic are owned by railroads. For instance, a public road that crosses railroad tracks may be owned by the railroad if built within the railroad right-of-way. Ownership in these cases depends on the agreements made between the political jurisdiction and the railroad. There are a small number of railroad-owned highway bridges in excess of 6 meters in total length in the inventory: 1,016 nationally. Bridges carrying railroads are not included in the database unless they also carry a public road or cross a public road where information of certain features, such as vertical or horizontal clearances, is required for management of the highway system.

A simple tabulation of the number of bridges by ownership does not take into account the traffic carried by the structure or the size of the structure. Exhibit 2-14 compares the ownership percentages based on the actual number of bridges with percentages based on average daily traffic on bridges and bridge deck area, respectively. Bridges owned by State agencies carry significantly higher cumulative traffic volumes than bridges owned by local agencies. State-owned bridges also tend to have greater deck area than locally owned bridges.

Exhibit 2-13 Bridges by Owner, 1996-2002
Number of Bridges by Year
Owner 1996 1998 2000 2002
Federal6,1717,7488,2219,371
State273,198273,897277,106280,266
Local299,078298,222298,889299,354
Private/Railroad2,3782,2782,2991,502
Unknown/Unclassified1,0371,1314151,214
Total581,862583,276586,930591,707
Source: National Bridge Inventory.
Q. How do the bridge ownership percentages compare with the road ownership percentages?
A.

The majority of bridges and roadways are owned by State and local agencies. The vast majority of roadways, however, are owned by local agencies. Bridge ownership is nearly equally divided between State ownership and local ownership. States tend to own larger, higher volume structures, such as those on Interstates and expressways. Localities own smaller structures on lower volume roadways, such as local roads and collectors.

Exhibit 2-14, percent bridge inventory, traffic and deck area by owner. Three pie charts, each with four segments. For bridge ownership, values are 1.6 percent Federal, 47.4 percent state, 50.6 percent local, and 0.5 percent other. For percentage of traffic carried, values are 0.2 percent Federal, 86.6 percent state, 12.6 percent local, and 0.6 percent other. For percentage of total deck area, values are 0.8 percent Federal, 75.2 percent state, 23.3 percent local, and 0.7 percent other. Source: National Bridge Inventory.

Q. If an agency owns a bridge, is it responsible for the maintenance and operation of the structure?
A.

Bridge maintenance and operation is the responsibility of the owner of the structure. Interagency agreements may be formed, such as those between State highway agencies and localities. In these cases, a secondary agency (such as the State) performs maintenance and operation work under agreement. This, however, does not transfer ownership and therefore does not negate the responsibilities of the bridge owners for maintenance and operation in compliance with Federal and State requirements.

Bridges by Functional Classification

Highway functional classifications are maintained with the NBI according to the hierarchy used for highway systems previously shown. The number of bridges by functional classification is summarized and compared with previous years in Exhibit 2-15. Overall percentages of each functional classification tend to remain relatively constant over time, although bridges are functionally reclassified as urban boundaries change.

Exhibit 2-15 Number of Bridges by        Functional System, 1996-2002
Functional Classification 1996 1998 2000 2002
Rural
Interstate 28,638 27,530 27,797 27,316
Other Arterial 72,970 73,324 74,796 74,814
Collector 144,246 143,140 143,357 144,101
Local 211,059 210,670 209,415 209,722
Subtotal 456,913 454,664 455,365 455,953
Urban
Interstate 26,596 27,480 27,882 27,929
Other Arterial 59,064 60,901 63,177 65,667
Collector 14,848 14,962 15,038 15,171
Local 24,441 24,962 25,684 26,609
Subtotal 124,949 128,305 131,781 135,376
Total 581,862 582,969 587,146 591,329
Source: National Bridge Inventory.

Exhibit 2-16 gives additional detail on bridges from the 2002 NBI dataset by cross tabulating the number of bridges by owner and functional classification. There are 378 structures (less than 0.1 percent) that do not have accurately coded functional classifications. These bridges are not included in the 2002 tabulation. Nearly all of the Interstate bridges are owned by State agencies (99.3 percent) with small numbers of Interstate bridges owned by other agencies, primarily in urban areas. Likewise, most of the bridges functionally classified as local (82.4 percent) are owned by cities, counties, townships, and other local agencies.

Exhibit 2-16 Bridges by Functional Classification and Owner, 2002
Functional Classification State Local Federal Private/
Railroad
Other/
Unclassified
All Owners
Rural
Interstate27,28310184127,316
Other Principal Arterials34,686300552915735,227
Minor Arterial36,6822,414402494039,587
Major Collector52,73741,742179853894,781
Minor Collector16,60231,4231,178892849,320
Local28,177173,5787,255564148209,722
Rural Total196,167249,4679,087820412455,953
Urban
Interstate27,601307291027,929
Other Freeway and Expressway15,42997024739616,844
Other Principal Arterial18,7855,317178010824,307
Minor Arterial11,93912,2884214610124,516
Collector5,0869,8502011410115,171
Local4,95621,0961952828026,609
Urban Total83,79649,828278678796135,376
Unclassified30359646378
TOTAL 280,266299,3549,3711,5021,214591,707
Source: National Bridge Inventory.

State agencies own the majority of bridges at the higher functional classifications and also own sizeable numbers of bridges across all functional classifications. Approximately 125,000 of the 280,000 State-owned bridges carry principal arterials including Interstates and other freeways and expressways. The remaining structures carry minor arterials, collectors, and local roadways. Of the nearly 300,000 locally owned bridges, the majority carry local roadways and collectors (93 percent). The majority of federal bridges (97 percent) are located in rural areas and carry either local or collector roadways (94 percent).

Exhibit 2-17 presents a summary of bridges and traffic carried by rural/urban status. Of all structures, 77.1 percent are located in rural areas. Though only 22.9 percent of the bridges are located in urban areas, these structures carry three-quarters of all daily traffic.

Exhibit 2-17, rural and urban bridges by number and percent of daily traffic, 2002. Bar chart. Values for rural bridges are 77.1 percent bridges and 26.7 percent of total daily traffic. Values for urban bridges are 22.9 percent of bridges and 73.3 percent of total daily traffic. Source: National Bridge Inventory.
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