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11 CHAPTER two State Of Practice In Bridge Management National Bridge Inspection Standards Items 2842: Functional or operational (capacity) information, design load Overview Items 4344: Structure/design/construction type and material of construction NBIS came about in the aftermath of the collapse of the Items 4556: Span information, geometric informa- Silver Bridge over the Ohio River between Ohio and West tion, and clearance dimensions (no Item 57) Virginia in 1967 (FHWA and FTA 2002, Chapter 11). This Items 5870: Structural condition and bridge loading failure, and the concerns it raised about bridge conditions information nationally and their implications for public safety, resulted in Items 7172: Waterway and approach data (no Items congressional mandates to the U.S.DOT in 1970 to develop 7374) and implement national bridge inspection standards and Items 7597: Inspector's work recommendations and procedures (P.L. 91-605). Subsequent federal surface trans- projected costs portation legislation during the next 35 years expanded the Items 98116: Other information of various categories inspection requirements and authorized federal funding to bridge programs (FHWA and FTA 2004, Exhibit 15-1). NBIS Several items have multiple parts (A, B, C), which requirements are issued as federal regulations (23 CFR Sub- accounts for the more than 125 entries. part C 650.300) that are updated by the FHWA from time to time in a formal rulemaking process that is published in Items relating to structural components and operational the Federal Register. The most recent NBIS update was in characteristics must be observed, assessed, and rated by cer- December 2004 (FHWA 2004). tified, trained inspectors. The FHWA Recording and Cod- ing Guide describes the alphanumeric codes that inspectors A core requirement of the NBIS is the biennial inspec- must use to rate each item. Rating systems for bridge condi- tion of all bridges and culverts greater than 20 ft in length tion and structural and functional appraisals are recorded on U.S. public roads. Bridges that have serious deficiencies on a scale from 0 to 9 (summarized in the following sec- are inspected more frequently, as required. Although select tions). The results of inspection ratings for all bridges on a bridges that are in excellent condition and meet certain other statewide network, plus local bridges within the state, are criteria may be inspected at intervals longer than 2 years with reported annually by each state DOT to the FHWA, where prior FHWA approval, only a small percentage of bridges they are compiled and processed within the National Bridge nationally, generally new bridges in excellent condition, Inventory (NBI) database. The NBI database is the source meet these criteria. Most bridges in the United States are of reports on national bridge statistics, including numbers inspected at at least 2-year intervals, and the biennial inspec- and percentages of bridges that are "structurally deficient" tion requirement of NBIS is widely understood throughout or "functionally obsolete," as explained later. The NBI the U.S. highway community. NBIS regulations also include database is also the source of data used by the FHWA in other provisions; for example, the required qualifications of its biennial report on bridge conditions and performance to inspection staff. the Congress (e.g., FHWA and FTA 2006, chapter 3). NBI ratings are described in some detail here because they play The practical guidelines for conducting NBIS-mandated a key role in federal bridge funding and state DOT track- bridge inspections are contained in a bridge recording and ing of bridge condition and performance. They are referred coding guide issued by the FHWA (1995). This guidebook to repeatedly in subsequent chapters as a key component of includes instructions and examples for more than 125 entries bridge management information. to be recorded, together with coding forms. An overview of the items addressed in the inspection guidelines is as follows: National Bridge Inventory Condition Ratings Items 127: General description and administrative The following scale is used to rate bridge condition (FHWA information 1995):

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12 9 = Excellent 2 = Basically intolerable, requiring a high priority 8 = Very Good of replacement 7 = Good 1 = This value of rating not used in appraisals 6 = Satisfactory 0 = Bridge closed 5 = Fair N = Not applicable 4 = Poor 3 = Serious Table 2 2 = Critical NBI RATINGS FOR BRIDGE DECKS, SUPERSTRUCTURE, 1 = "Imminent" Failure AND SUBSTRUCTURE 0 = Failure N = Not Applicable Rating General Description of Condition 9 EXCELLENT CONDITION For example, the condition of new, well-constructed bridges would be taken as 9. Ratings from 8 to 6 would 8 VERY GOOD CONDITION: no problems noted. characterize generally good performance, with only minor 7 GOOD CONDITION: some minor problems. problems. Ratings from 5 to 3 are intended as warnings of growing problems that require action, whether (1) mainte- 6 SATISFACTORY CONDITION: structural elements nance, rehabilitation, or replacement; (2) posting of load show some minor deterioration. limits to prohibit heavy vehicles; or (3) increased frequency FAIR CONDITION: all primary structural elements of inspection. Some agencies assign "flags" to these ratings 5 are sound but may have minor section loss, cracking, to highlight these warnings for managers. Ratings of 2 or 1 spalling, or scour. are critical and call for immediate action, including possible 4 POOR CONDITION: advanced section loss, deteriora- bridge closure. A rating of 0 denotes a failed bridge that is tion, spalling, scour. out of service and cannot be repaired. N means that the par- SERIOUS CONDITION: loss of section, deterioration, ticular item is not applicable to that bridge. These general spalling, or scour have seriously affected primary struc- 3 descriptions introduce the rating scale; the actual inspec- tural components. Local failures are possible. Fatigue cracks in steel or shear cracks in concrete may be present. tion and rating process uses more specific definitions and explanations that are tailored to particular inspection items. CRITICAL CONDITION: advanced deterioration of primary structural elements. Fatigue cracks in steel or For example, Table 2 gives rating definitions for Inspection shear cracks in concrete may be present or scour may items 58-Bridge Decks, 59-Superstructure, and 60-Sub- 2 have removed substructure support. Unless closely structure. For comparison, Table 3 lists rating definitions for monitored, it may be necessary to close the bridge until item 62, Culverts. corrective action is taken. "IMMINENT" FAILURE CONDITION: major deteri- National Bridge Inventory Appraisal Ratings oration or section loss present in critical structural com- 1 ponents or obvious vertical or horizontal movement Appraisal ratings differ from the condition ratings. Appraisal affecting structural stability. Bridge is closed to traffic but corrective action may put back in light service. items evaluate the level of service provided by a bridge to the highway it serves, as compared with that of a new bridge FAILED CONDITION: out of service--beyond cor- 0 built to current design standards that are now applicable to rective action. that highway. Appraisals can apply to structural as well as N Not applicable. functional items. Unlike condition ratings that are recorded Source: FHWA 1995. by an inspector, appraisal items are computed by FHWA's NBI Edit/Update Program based on values of two or more other NBI rating items. The rating scale for appraisals is as Structural Deficiency and Functional Obsolescence follows (FHWA 1995): The NBI ratings are used to compute two measures of defi- 9 = Superior to present desirable criteria ciency in bridge condition and performance: Structural 8 = Equal to present desirable criteria Deficiency (SD) and Functional Obsolescence (FO). These 7 = Better than present minimum criteria designations are important because (1) they call attention 6 = Equal to present minimum criteria to important bridge structural or functional needs; (2) they 5 = Somewhat better than minimum adequacy to shape the public's and stakeholders' perceptions of bridge tolerate being left in place as is condition and performance that are obtained from annual 4 = Meets basic minimum tolerable limits to be left statistical summaries of NBI data and the biennial bridge in place as is Conditions and Performance report to Congress; and (3) 3 = Basically intolerable, requiring a high priority they are part of the discussions of bridge program funding at of corrective action federal, state, and local levels.

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13 Table 3 rated poor or worse. The structural rating items used to eval- NBI RATINGS FOR CULVERTS uate bridge deficiency are listed in Table 4. The conditions of bridge structures are rated using Items 5860; the condition Rating General Description of Condition of culverts more than 20 ft in length are rated by Item 62. 9 No deficiencies. The criteria for poor or worse are also shown in Table 4 in terms of NBI rating values. The implications of this rating 8 No noticeable or noteworthy deficiencies that affect the condition of the culvert. Insignificant scrape marks approach are that (1) a designation of SD may be triggered by caused by drift. any one of the items in Table 4, (2) a bridge rated as SD does Shrinkage cracks, light scaling, and insignificant spall- not differentiate whether only one or many items in Table 4 ing that does not expose reinforcing steel. Insignificant were rated poor, and (3) an SD classification does not convey damage caused by drift with no misalignment and not the causes of the poor ratings. Recent congressional testi- 7 requiring corrective action. Some minor scouring has mony has described, for example, how poor ratings might occurred near curtain walls, wingwalls, or pipes. Metal culverts have a smooth symmetrical curvature with result from deficiencies that do not reflect overall bridge superficial corrosion and no pitting. structural integrity (Bizjak 2007; Kerley 2007, p. 7). SD is Deterioration or initial disintegration, minor chloride thus a coarse measure. SD signals a bridge problem requir- contamination, cracking with some leaching, or spalls ing further attention, but in and of itself does not communi- 6 on concrete or masonry walls and slabs. Local minor cate details of the causes or implications of poor rating(s). scouring at curtain walls, wingwalls, or pipes. Metal culverts have a smooth curvature, nonsymmetrical Table 4 shape, significant corrosion, or moderate pitting. STRUCTURAL DEFICIENCY CRITERIA Moderate to major deterioration or disintegration, extensive cracking and leaching, or spalls on concrete NBI Rating Structural Item Type of Criterion for or masonry walls and slabs. Minor settlement or mis- Item Number Rated Rating Poor or Worse 5 alignment. Noticeable scouring or erosion at curtain walls, wingwalls, or pipes. Metal culverts have signifi- 58 Deck rating Condition <5 cant distortion and deflection in one section, significant corrosion, or deep pitting. 59 Superstructure Condition <5 rating Large spalls, heavy scaling, wide cracks, considerable efflorescence, or opened construction joint permitting Substructure 60 Condition <5 loss of backfill. Considerable settlement or misalign- rating 4 ment. Considerable scouring or erosion at curtain 62 Culvert rating Condition <5 walls, wingwalls, or pipes. Metal culverts have signifi- cant distortion and deflection throughout, extensive Structural 67 Appraisal <3 corrosion, or deep pitting. evaluation Any condition described in Code 4 but which is exces- Waterway sive in scope. Severe movement or differential settle- 71 Appraisal <3 adequacy ment of the segments, or loss of fill. Holes may exist in walls or slabs. Integral wingwalls nearly severed from Note: FHWA and FTA 2006. 3 culvert. Severe scour or erosion at curtain walls, wing- walls, or pipes. Metal culverts have extreme distortion and deflection in one section, extensive corrosion, or The FHWA has observed that the primary reason to clas- deep pitting with scattered perforations. sify bridges as structurally deficient is a low condition rating. Integral wingwalls collapsed; severe settlement of Eighty percent of structurally deficient bridges nationwide roadway due to loss of fill. Section of culvert may have failed and can no longer support embankment. Com- are so classified because of their condition ratings; 20%, 2 plete undermining at curtain walls and pipes. Correc- because of their appraisals (FHWA and FTA 2006). The two tive action required to maintain traffic. Metal culverts are not mutually exclusive--that is, a bridge may be defi- have extreme distortion and deflection throughout with cient in both its condition rating and its appraisal. extensive perforations due to corrosion. Bridge closed. Corrective action may put back in light Functional Obsolescence 1 service. 0 Bridge closed. Replacement necessary. An inspected bridge is functionally obsolete if-- N Not applicable--used if structure is not a culvert. Source: FHWA 1995. it is not already structurally deficient; and it is deficient in terms of its geometry, clearance, or load capacity. Structural Deficiency The NBI rating items that are considered when determin- An inspected bridge is structurally deficient if at least one ing FO and the criteria used to determine whether an item structural rating item, whether condition or appraisal, is is deficient are shown in Table 5. With one exception, these

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14 appraisal items are all computed from other NBI item ratings Special Reductions, S4 a deduction from SR, maxi- by the NBI Edit/Update Program. mum absolute value = 13 Table 5 Each of these rating components is defined here. Figure 2 FUNCTIONAL OBSOLESCENCE CRITERIA provides a graphic representation of these SR components. Note that the structural and the functional components of NBI Rating Criterion for Item Number Functional Item Rated Poor or Worse SR, S1, and S2, respectively, are different from SD and FO in the preceding section. 67 Structural evaluation =3 (function of load capacity) 68 Deck geometry <4 Underclearance (over 69 <4 highway) 71 Waterway adequacy =3 Approach roadway 72 <4 alignment Note: FHWA and FTA 2006. Rating items 67 and 71 overlap the structural and func- tional evaluations (see Tables 4 and 5). If either of these rat- ings equals 3, then the bridge is not considered structurally deficient, because the problem can still be corrected (refer to the definition of the nine-point appraisal scale mentioned earlier). However, because a rating of 3 implies that bridge load capacity or waterway adequacy is too low to be toler- able, the bridge is characterized as functionally obsolete. If either of these ratings falls below 3, the bridge is considered structurally deficient (FHWA and FTA 2006). Item 72, Approach Roadway Alignment, is an excep- FIGURE 2 Sufficiency rating components (Source: FHWA 1995). tion to the explanation of appraisal items described earlier. Note: Obs. = Obsolescence; Rdwy. = Roadway; STRAHNET = Rather than comparing this alignment with current design Strategic Highway Network. standards, the existing approach alignment is compared with the existing bridge alignment. Ratings are assigned based Structural Adequacy and Safety, S1, is a function of on the ability of the two alignments, functioning together, the following rating items: to permit traffic to enter the bridge without significant speed Item 59, Superstructure; reduction. Item 60, Substructure; Item 62, Culverts; and If a bridge's ratings are such that it is both structurally Item 66, Inventory rating (a measure of load deficient and functionally obsolete, it is reported in the NBI capacity). database as structurally deficient. SD takes precedence over Serviceability and FO, S2, is a function of the follow- FO in reporting bridge status. A bridge is listed as function- ing rating items: ally obsolete only if it is not structurally deficient. Item 28, Number of lanes on the structure; Item 29, Average daily traffic (ADT); Sufficiency Rating Item 32, Approach roadway width; Item 43, Structure type, main; The Sufficiency Rating (SR) ranges from a value of 100 Item 51, Bridge roadway width; (best) to 0 (worst). It includes four rating components Item 53, Vertical clearance over deck; (FHWA 1995): Item 58, Deck condition; Item 67, Structural evaluation (a function of load Structural Adequacy and Safety, S1 maximum value capacity); = 55 Item 68, Deck geometry; Serviceability and FO, S2 maximum value = 30 Item 69, Underclearance; Essentiality for Public Use, S3 maximum value = 15 Item 71, Waterway adequacy;

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15 Item 72, Approach roadway alignment; and functional classes, traffic levels, and construction materials. Item 100, STRAHNET (Strategic Highway The requirement for state DOTs, working with local govern- Network) Designation (a network comprising about ments, to inspect bridges periodically and submit NBI data 61,000 miles, including the Interstate system, to to the FHWA annually ensures a nationwide consistency of serve national defense needs). method, a wide familiarity with NBI data and ratings, and a Essentiality for Public Use, S3, is a function of the comprehensive, up-to-date database. NBI bridge ratings are ratings of the following bridge items: specified at an aggregate level of structural component and are Item 19, Detour length; analytically simple. These characteristics are advantages in Item 29, ADT; and that they enable the NBIS to apply to a numerous and diverse Item 100, STRAHNET Highway Designation. nationwide bridge population. Because the approach depends Special Reductions, S4, are a function of the ratings of on the skill and training of the certified bridge inspectors, items listed here. A Special Reduction is applied only this factor is addressed in detail in the federal regulations that when S1 + S2 + S3 50; otherwise S4 = 0. Relevant govern the NBIS (23 CFR 650C). The FHWA has updated bridge items are: the NBIS rating items from time to time to address new prob- Item 19, Detour length; lems--for example, the need for underwater inspections to Item 36, Traffic safety features; and protect bridges from scour, and the identification and need Item 43, Structure type, main. for inspection of fracture-critical members that, if degraded, could make the bridge vulnerable to further structural dam- The rating components S1 through S4 are computed by a age. Since its inception in the 1970s, the NBI database has set of analytic procedures in the NBI database as a function compiled a detailed history of every bridge carrying a public of the respective NBI ratings listed earlier (FHWA 1995). highway in the United States, making it the most comprehen- sive and uniformly organized source of bridge condition data The SR is the total of S1 through S4: SR = S1 + S2 + S3 S4, in the country. The NBI data are the basis of FHWA's identifi- where S4 represents a deduction. When all the NBI ratings cation of bridge needs, allocation of bridge program funding, listed earlier for S1, S2, and S3 are at their maximum (best and biennial reporting to Congress. possible) value, SR = S1 + S2 + S3 = 100, assuming S4 = 0. As bridge structural, functional, or public use ratings decline, The NBI database and the computed SD, FO, and SR rat- the values of S1, S2, and S3 decline from their maximum val- ings have provided current and comprehensive data on bridge ues and SR < 100. By correcting structural problems, defi- status and investment needs during the last 35 years. Today, cient geometry, or other problems represented in the rating however, the deficiency and sufficiency ratings are recog- items, bridge projects can restore SR to a higher value. With- nized to have shortcomings when applied to management or out any corrective measures, SR theoretically will continue funding decisions. This chapter covers those shortcomings to decline to its minimum (zero) value, at which point the related to how the NBI ratings are formulated. Chapter three bridge is no longer in service. If a bridge has an attribute discusses how DOTs are working to compensate for short- that causes a Special Reduction--for example, a long detour comings in NBI-rating decision support. Chapter four recaps route--its SR can never be at the theoretical maximum-- key issues regarding NBI deficiency and sufficiency ratings that is, SR < 100 even when the bridge is new. that were presented in recent congressional testimony. These various concerns can be summarized as follows: Implications for Bridge Management and Program Funding The SD and FO ratings are coarse: Although they signal a potential problem, they do not distinguish between The NBI measures of SD, FO, and SR are important to single versus multiple causes or their possible impacts, bridge management and to federal funding of bridge pro- as discussed earlier. grams. The FHWA lists the number and percentage of SD The SD, FO, and SR ratings are reactive; that is, they and FO bridges on its website, and many agencies track these do not signal a bridge problem until it has already measures as key indicators of the success of their bridge pro- occurred. Moreover, they do not show an improved grams. Table 6 gives these statistics for each state as of 2007, bridge condition unless corrective or remedial work including bridges on National Highway System (NHS) as is done. They are therefore unsuited to preventive well as non-NHS highways. maintenance strategies that could prevent or forestall bridge damage before it occurs and that could be more NBI Ratings as Performance Indicators economical. The weights and formulas used to compute SRs are The NBIS system of coding and recording bridge condition fixed and may be arbitrary as bridge designs, con- was designed to apply to the entire public highway bridge struction materials, vehicle loads, bridge investment inventory in the United States. The NBI database currently strategies and priorities, and other factors continue to includes almost 600,000 bridges of various designs, highway evolve.

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16 Table 6 NBI STATISTICS ON BRIDGE DEFICIENCY, 2007 No. of Bridges No. of SD No. of FO No. SD or FO Percent SD or FO Alabama 15,881 1,899 2,158 4,057 25.5% Alaska 1,229 155 179 334 27.2% Arizona 7,348 181 600 781 10.6% Arkansas 12,531 997 1,908 2,905 23.2% California 24,184 3,140 3,837 6,977 28.8% Colorado 8,366 580 824 1,404 16.8% Connecticut 4,175 358 1,042 1,400 33.5% Delaware 857 20 112 132 15.4% Dist. of Columbia 245 24 128 152 62.0% Florida 11,663 302 1,692 1,994 17.1% Georgia 14,563 1,028 1,888 2,916 20.0% Hawaii 1,115 142 358 500 44.8% Idaho 4,104 349 452 801 19.5% Illinois 25,998 2,501 1,840 4,341 16.7% Indiana 18,494 2,030 2,004 4,034 21.8% Iowa 24,776 5,153 1,455 6,608 26.7% Kansas 25,461 2,991 2,372 5,363 21.1% Kentucky 13,637 1,362 2,928 4,290 31.5% Louisiana 13,342 1,780 2,180 3,960 29.7% Maine 2,387 349 468 817 34.2% Maryland 5,127 388 980 1,368 26.7% Massachusetts 5,018 585 1,987 2,572 51.3% Michigan 10,923 1,584 1,304 2,888 26.4% Minnesota 13,067 1,156 423 1,579 12.1% Mississippi 17,007 3,002 1,315 4,317 25.4% Missouri 24,071 4,433 3,108 7,541 31.3% Montana 4,980 473 541 1,014 20.4% Nebraska 15,475 2,382 1,241 3,623 23.4% Nevada 1,705 47 156 203 11.9% New Hampshire 2,364 383 358 741 31.3% New Jersey 6,448 750 1,501 2,251 34.9% New Mexico 3,850 404 294 698 18.1% New York 17,361 2,128 4,518 6,646 38.3% North Carolina 17,783 2,272 2,787 5,059 28.4% North Dakota 4,458 743 249 992 22.3% Ohio 27,998 2,862 4,001 6,863 24.5% Oklahoma 23,524 5,793 1,614 7,407 31.5% Oregon 7,318 514 1,155 1,669 22.8% Pennsylvania 22,325 5,802 3,934 9,736 43.6%

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17 Table 6 (Continued) NBI STATISTICS ON BRIDGE DEFICIENCY, 2007 No. of Bridges No. of SD No. of FO No. SD or FO Percent SD or FO Rhode Island 748 164 232 396 52.9% South Carolina 9,221 1,260 808 2,068 22.4% South Dakota 5,924 1,216 261 1,477 24.9% Tennessee 19,838 1,325 2,776 4,101 20.7% Texas 50,271 2,186 7,851 10,037 20.0% Utah 2,851 233 254 487 17.1% Vermont 2,712 500 467 967 35.7% Virginia 13,417 1,208 2,234 3,442 25.7% Washington 7,651 400 1,661 2,061 26.9% West Virginia 7,001 1,058 1,515 2,573 36.8% Wisconsin 13,798 1,302 789 2,091 15.2% Wyoming 3,030 389 231 620 20.5% Puerto Rico 2,146 241 822 1,063 49.5% Totals 599,766 72,524 79,792 152,316 25.4% Source: FHWA 2007b. Note: Table for 2007. Data reflect bridges on NHS and non-NHS highways. SD = structurally deficient; FO = functionally obsolete. The SD and SR ratings are somewhat inconsistent with The FHWA specifies four criteria based on NBI data that respect to bridge decks. Although SD directly reflects a must all be met for a bridge to qualify for federal Highway deck condition that is poor or worse, the SR is much less Bridge Program (HBP) funding (FHWA 2006): sensitive: A deduction for poor or worse deck condition in the Serviceability and FO calculation subtracts at The bridge must be longer than 20 ft (NBI Item 49), most 3% to 5% from the SR value. Moreover, deck con- be a highway bridge that carries a public road, and be dition is not included in the Structural Adequacy and included in the NBI database. Safety component of SR. The bridge must be classified as either structurally No generally accepted and used set of predictive models deficient or functionally obsolete. exists for SD, FO, and SR. The models that have been The bridge must have an SR of 80 or less to qualify for developed to date are for specific agencies and purposes federally funded rehabilitation, or an SR of less than 50 as discussed later and are not in general use. Lacking to be eligible for federal funding of its replacement. such deterioration or performance models, agencies can- The bridge cannot have been built or replaced (NBI not forecast trends in deterioration of SD, FO, and SR. Item 27) or rehabilitated or reconstructed (NBI Item The lack of such models precludes using NBI ratings 106) within the last 10 years, regardless of the source to predict future bridge needs; quantify the benefits of of funding (the "10-year rule"). future bridge investments; analyze different scenarios regarding infrastructure policy, performance, and cost; The requirements for an SD or FO rating and the SR and assess resource allocation trade-offs. thresholds were an attempt to give greatest priority to those bridges that had greatest need for work (essentially a "worst- Chapter three provides examples of other technical mea- first" criterion) (23 CFR 650D). The FHWA imposed the sures of bridge condition and performance that DOTs have 10-year rule "[to prevent] a bridge from remaining in a defi- developed to overcome some of these drawbacks. cient classification after major reconstruction and thereby affecting the bridge fund apportionments to a State" (FHWA Funding Implications n.d.). Recently, the FHWA has clarified these provisions with respect to the eligibility of structurally deficient bridge decks Utilization of the NBI as the primary data source for the disbursement of funds through HBRRP [Highway for HBP funding (Lwin 2007). Structurally deficient bridge Bridge Replacement and Rehabilitation Program, now the decks that require rehabilitation or replacement are eligible Highway Bridge Program] and the Special Bridge Program for federal funding regardless of the bridge's SR or require- has been the basis for bridge management decision making ments of the 10-year rule, consistent with the provisions of since the early 1970s (Small et al. 1999, A-1/2).