Synthesis of National and International 

Methodologies Used for Bridge

Health Indices 

PUBLICATION NO. FHWA-HRT-15-081 MAY 2016

Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296
FOREWORD

This study was conducted as part of the Federal Highway Administration’s Long-Term Bridge 

Performance (LTBP) Program. The LTBP Program is a long-term research effort, authorized by 

the U.S. Congress under The Safe, Accountable, Flexible, Efficient Transportation Equity Act

legislation, to collect high-quality bridge data from a representative sample of highway bridges 

nationwide that will help the bridge community to better understand bridge performance. This 

report reviews the state-of-the-art with respect to bridge condition indices being used to assess 

performance of bridges in the United States and other countries. This report should be of interest 

to bridge program personnel from Federal, State, and local transportation departments as well as 

to parties engaged in bridge-related research.

Mark Swanlund

Acting Director, Office of Infrastructure

 Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

in the interest of information exchange. The U.S. Government assumes no liability for the use of 

the information contained in this document. This report does not constitute a standard, 

specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or 

manufacturers’ names appear in this report only because they are considered essential to the 

objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve 

Government, industry, and the public in a manner that promotes public understanding. Standards 

and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its 

information. FHWA periodically reviews quality issues and adjusts its programs and processes to 

ensure continuous quality improvement.
TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.

FHWA-HRT-15-081

2. Government Accession No.

N/A

3. Recipient’s Catalog No.

N/A

4. Title and Subtitle

Synthesis of National and International Methodologies 

Used for Bridge Health Indices

5. Report Date

May 2016

6. Performing Organization Code: 

N/A

7. Author(s)

Chase, S.B., Adu-Gyamfi, Y., Aktan, A.E., and Minaie, E.

8. Performing Organization Report No. 

N/A

9. Performing Organization Name and Address

Pennoni Associates Inc.

One Drexel Plaza

3001 Market Street, Second Floor

Philadelphia, PA 19104-2897

10. Work Unit No.

N/A

11. Contract or Grant No.

DTFH61-12-D-00030-T-13002

12. Sponsoring Agency Name and Address

Office of Infrastructure Research and Development

Federal Highway Administration

6300 Georgetown Pike

McLean, VA 22101-2296

13. Type of Report and Period Covered

Literature Review

14. Sponsoring Agency Code

HRDI-50

15. Supplementary Notes

FHWA contacts: Susan Lane, HRDI-50, and Yamyra Rodriguez-Otero, HRDI-50.

16. Abstract

Bridge performance measures are important components of any successful Bridge Management System. 

Different types of performance measures have been developed for various purposes. The types of performance 

measures are usually a reflection of an agency’s goals. The bridge health or condition index is a type of 

performance measure used by agencies interested in preserving the condition of bridge structures. Bridge 

condition index is very attractive because it provides a single index for assessment of the structural and or 

functional health of a bridge based on the condition of the bridge’s structural elements and the services 

provided by the bridge. As outlined in the FHWA’s Long-Term Bridge Performance Program, the development 

of condition indices should be driven by more objective and quantitative data to help bridge managers make 

informed decisions. This work reviews the state-of-the-art with respect to bridge condition indices being used to 

assess performance of bridges in the United States and other countries.

17. Key Words

LTBP Program, bridge management, 

performance measures, health index

18. Distribution Statement

No restrictions. This document is available through the 

National Technical Information Service, Springfield, VA 

22161.

http://www.ntis.gov

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

52

22. Price

N/A

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized.
ii

SI* (MODERN METRIC) CONVERSION FACTORS 

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol 

LENGTH

in inches 25.4 millimeters mm 

ft feet 0.305 meters m 

yd yards 0.914 meters m 

mi miles 1.61 kilometers km 

AREA 

in2 square inches 645.2 square millimeters mm2

ft2 square feet 0.093 square meters m2

yd2 square yard 0.836 square meters m2

ac acres 0.405 hectares ha

mi2 square miles 2.59 square kilometers km2

VOLUME 

fl oz fluid ounces 29.57 milliliters mL 

gal gallons 3.785 liters L 

ft3 cubic feet 0.028 cubic meters m3 

yd3 cubic yards 0.765 cubic meters m3 

NOTE: volumes greater than 1000 L shall be shown in m3

MASS oz ounces 28.35 grams g

lb pounds 0.454 kilograms kg

T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t") 

TEMPERATURE (exact degrees) o

F Fahrenheit 5 (F-32)/9 Celsius o

C 

or (F-32)/1.8 

ILLUMINATION 

fc foot-candles 10.76 lux lx

fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS 

lbf poundforce 4.45 newtons N 

lbf/in2 poundforce per square inch 6.89 kilopascals kPa 

APPROXIMATE CONVERSIONS FROM SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

LENGTH mm millimeters 0.039 inches in 

m meters 3.28 feet ft 

m meters 1.09 yards yd 

km kilometers 0.621 miles mi 

AREA mm2 square millimeters 0.0016 square inches in2 

m2 square meters 10.764 square feet ft2 

m2 square meters 1.195 square yards yd2 

ha hectares 2.47 acres ac

km2 square kilometers 0.386 square miles mi2 

VOLUME 

mL milliliters 0.034 fluid ounces fl oz 

L liters 0.264 gallons gal 

m3 cubic meters 35.314 cubic feet ft3 

m3 cubic meters 1.307 cubic yards yd3 

MASS 

g grams 0.035 ounces oz

kg kilograms 2.202 pounds lb

Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T 

TEMPERATURE (exact degrees) o

C Celsius 1.8C+32 Fahrenheit oF 

ILLUMINATION 

lx lux 0.0929 foot-candles fc 

cd/m2 candela/m2 0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS 

N newtons 0.225 poundforce lbf 

kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. 

(Revised March 2003)
iii

TABLE OF CONTENTS

CHAPTER 1. REVIEW OF METHODOLOGIES USED FOR BRIDGE HEALTH 

INDICES (BHIs) ..................................................................................................................... 1

INTRODUCTION .................................................................................................................... 1

CHAPTER 2. RATIO-BASED CONDITION INDEX.............................................................. 5

COMPUTATIONAL APPROACH OVERVIEW................................................................. 5

DATA INVENTORY AND CONDITION RATINGS .......................................................... 5

Element-Level Condition Data ............................................................................................... 5

Element Failure or Replacement Cost Data............................................................................ 6

Calculating the California BHI............................................................................................... 6

STRENGTHS AND LIMITATIONS...................................................................................... 7

Strengths ................................................................................................................................. 7

Limitations.............................................................................................................................. 8

CHAPTER 3. WEIGHTED AVERAGE APPROACHES........................................................ 9

COMPUTATIONAL APPROACH OVERVIEW................................................................. 9

UNITED KINGDOM’S BCI.................................................................................................... 9

Calculating British BCI........................................................................................................... 9

SOUTH AFRICA’S BCI........................................................................................................ 12

Condition Ratings ................................................................................................................. 12

Calculating South African BCI............................................................................................. 12

AUSTRALIA’S BCN.............................................................................................................. 13

Calculating Australian BCN ................................................................................................. 13

AUSTRIA’S BCI..................................................................................................................... 15

Calculating Austrian BCI...................................................................................................... 15

FINLAND’S BCI..................................................................................................................... 15

Calculating Finnish BCI ....................................................................................................... 15

STRENGTHS AND LIMITATIONS.................................................................................... 17

Strengths ............................................................................................................................... 17

Limitations............................................................................................................................ 17

CHAPTER 4. WORST-CONDITIONED COMPONENT APPROACHES......................... 19

COMPUTATIONAL APPROACH OVERVIEW............................................................... 19

GERMANY’S BCI.................................................................................................................. 19

Calculating German BCI....................................................................................................... 21

JAPAN’S BCI.......................................................................................................................... 23

Calculating Japanese BCI ..................................................................................................... 23

STRENGTHS AND LIMITATIONS.................................................................................... 24

Strengths ............................................................................................................................... 24

Limitations............................................................................................................................ 24
iv

CHAPTER 5. QUALITATIVE METHODS............................................................................ 25

COMPUTATIONAL APPROACH OVERVIEW............................................................... 25

AUSTRALIA’S BRIDGE HEALTH INDICATOR............................................................ 25

AUSTRIA’S QUALITATIVE BRIDGE RATING.............................................................. 25

STRENGTHS AND LIMITATIONS.................................................................................... 26

Strengths ............................................................................................................................... 26

Limitations............................................................................................................................ 26

CHAPTER 6. OTHER METHODS.......................................................................................... 27

BRIDGE SR............................................................................................................................. 27

Data Inventory and Condition Rating................................................................................... 27

Functional Information ......................................................................................................... 27

Operational Condition Information....................................................................................... 27

Condition Information .......................................................................................................... 27

Calculating SR ...................................................................................................................... 29

Uses of SR............................................................................................................................. 29

RISK-BASED PRIORITIZATION FOR BRIDGES .......................................................... 29

Definition of Risk ................................................................................................................. 29

Risk-Based Assessment Framework..................................................................................... 33

Strengths and Limitations..................................................................................................... 39

CHAPTER 7. CONCLUSIONS................................................................................................. 41

REFERENCES............................................................................................................................ 43
v

LIST OF FIGURES

Figure 1. Equation. Condition state WF ......................................................................................... 6

Figure 2. Equation. TEV................................................................................................................. 7

Figure 3. Equation. CEV................................................................................................................. 7

Figure 4. Equation. BHI.................................................................................................................. 7

Figure 5. Equation. ECF (“high” element importance) ................................................................ 10

Figure 6. Equation. ECF (“medium” element importance) .......................................................... 10

Figure 7. Equation. ECF (“low” element importance) ................................................................. 11

Figure 8. Equation. ECI................................................................................................................ 11

Figure 9. Equation. BCS ............................................................................................................... 11

Figure 10. Equation. BCI.............................................................................................................. 11

Figure 11. Equation. Defect condition index................................................................................ 12

Figure 12. Equation. Bridge importance factor ............................................................................ 13

Figure 13. Equation. Final bridge condition ................................................................................. 13

Figure 14. Illustration. Three-level hierarchy for calculating Australian BCN............................ 13

Figure 15. Equation. ACR for each element................................................................................. 14

Figure 16. Equation. AGR for each structural group/category..................................................... 14

Figure 17. Equation. BCN ............................................................................................................ 14

Figure 18. Equation. Overall bridge condition rating................................................................... 15

Figure 19. Equation. Repair index ................................................................................................ 17

Figure 20. Equation. Component group........................................................................................ 22

Figure 21. Equation. Component group condition index.............................................................. 22

Figure 22. Equation. German BCI................................................................................................ 22

Figure 23. Equation. Demerit ratings............................................................................................ 24

Figure 24. Equation. SR................................................................................................................ 29

Figure 25. Equation. Perceived relative risk................................................................................. 30

Figure 26. Chart. Risk scale for risk-based prioritization framework .......................................... 32

Figure 27. Flowchart. Proposed risk-based assessment framework ............................................. 33
vi

LIST OF TABLES

Table 1. Summary of BHIs and their calculation approaches ........................................................ 3

Table 2. Sample element-level inspection data............................................................................... 6

Table 3. WFs for each condition state ............................................................................................ 7

Table 4. Extent descriptions............................................................................................................ 9

Table 5. Severity descriptions......................................................................................................... 9

Table 6. ECS ................................................................................................................................. 10

Table 7. EIF .................................................................................................................................. 10

Table 8. BCI condition.................................................................................................................. 11

Table 9. DER rating values........................................................................................................... 12

Table 10. Decisionmaking with BCN........................................................................................... 14

Table 11. Structural component weights ...................................................................................... 16

Table 12. Condition ratings........................................................................................................... 16

Table 13. Repair urgency.............................................................................................................. 16

Table 14. Damage severity ........................................................................................................... 16

Table 15. Damage ratings for structural stability.......................................................................... 19

Table 16. Damage ratings for traffic safety .................................................................................. 20

Table 17. Damage ratings for durability....................................................................................... 20

Table 18. Damage condition ratings............................................................................................. 21

Table 19. Identified damage values.............................................................................................. 21

Table 20. Values of 2 for substructure component groups......................................................... 22

Table 21. Values of 2 or other component groups ..................................................................... 22

Table 22. Values of 3.................................................................................................................. 23

Table 23. List of deficiency ratings .............................................................................................. 23

Table 24. Deficiency ratings and reducing ratios ......................................................................... 24

Table 25. Bridge condition description based on element importance and condition states........ 25

Table 26. Description of condition ratings for bridge elements in Austria’s qualitative 

approach.................................................................................................................................. 26

Table 27. NBI condition ratings.................................................................................................... 28

Table 28. Summary of relevant performance limit states, hazards, vulnerabilities, and 

exposures for bridges.............................................................................................................. 31

Table 29. Risk assessment levels.................................................................................................. 34

Table 30. Preliminary hazard values for level 1 and 2 risk assessments...................................... 34

Table 31. Preliminary vulnerability values for level 1 and 2 risk assessment.............................. 35

Table 32. Preliminary exposure levels for level 1 and 2 risk assessments................................... 38

Table 33. Preliminary risk levels.................................................................................................. 38

Table 34. Preliminary assessment programs per risk level........................................................... 39

∆

∆

∆
vii

LIST OF ABBREVIATIONS

AASHTO American Association of State Highway and Transportation Officials

ACR average condition rating

ADT average daily traffic

ADTT average daily truck traffic

AGR average group rating

BCFS Bridge Condition Forecasting System

BCI bridge condition index

BCN bridge condition number

BCS bridge condition score

BHI bridge health index

BMS bridge management system

BrM AASHTOWareTM Bridge Management software

CEV current element value

DER degree, extent, and relevancy

ECF element condition factor

ECS element condition score

EIF element importance factor

FC failure cost

FHWA Federal Highway Administration

Finnra Finnish Road Administration

LTBP Long-Term Bridge Performance

MAP-21 Moving Ahead for Progress in the 21st Century

NBI National Bridge Inventory

NDE nondestructive evaluation

NJDOT New Jersey Department of Transportation

SR sufficiency rating

TEQ total element quantity

TEV total element value

UBHI universal bridge health index

VicRoads Roads Corporation of Victoria

WF weighting factor

1

CHAPTER 1. REVIEW OF METHODOLOGIES USED FOR BRIDGE HEALTH 

INDICES (BHIs)

INTRODUCTION

Bridge performance measures are an important component of any successful bridge management 

system (BMS). They can be used as a tool for communicating with legislatures, bridge managers,

and, most importantly, the public on issues such as traffic safety and structural vulnerability of 

bridges to disasters such as earthquakes, scour, etc.(1,2) Different types of performance measures 

have been developed for various purposes. The type of performance measure is usually a 

reflection of the agency goals. A bridge health or condition index is used as a performance 

measure by agencies interested in preserving the condition of bridge structures or prioritizing the 

maintenance or replacement projects within their bridge inventory. Other performance measures,

such as geometric and inventory ratings, are used to improve traffic safety of a bridge. 

Vulnerability and/or resiliency ratings are examples of performance measures used to show how 

vulnerable bridge structures are to structural or operational hazards such as hurricanes, 

earthquakes, or over-load trucks and how well they perform in these situations. 

The bridge condition or health index is a useful tool for assessing the structural or functional 

health of a bridge. The index is calculated based on the condition of the bridge’s structural 

elements and the service provided by the bridge. For the purposes of bridge management, the 

most important use of a BHI is to identify which structures in the inventory are the most 

deteriorated and are most urgently in need of repair work. Most BMSs also use a bridge 

condition index (BCI) to help track the general system condition over time, evaluate the benefits 

of an agency’s bridge maintenance and rehabilitation programs, and serve as a basis for 

allocating resources to bridges within a network.

The increased availability of element-level inspection information influenced the redevelopment 

of BHIs used around the globe. Currently, most BMSs rely on element-level information for 

calculating BHIs.

(2,3) Based on the computational approach used, current methods for developing 

condition or health indices can be grouped into the following four approaches:

• Ratio-based methods assign a BCI or bridge condition number (BCN) based on the ratio 

of the current condition to the condition of the structure when it was new. The objective 

for this method is to calculate the remaining value of the bridge. The California BHI and 

the health index method used by AASHTOWARETM Bridge Management software, BrM 

(formerly Pontis),1 are the examples for ratio-based methods discussed in this report. 

• The weighted averaging approach is suitable for planning bridge maintenance and 

rehabilitation activities. The approach estimates the condition of the whole structure by 

combining condition ratings of all individual bridge elements weighted by their 

significance or contribution to the structural integrity of the bridge. This approach is 

 1

BrM is a BMS sold and maintained by the American Association of State Highway and Transportation Officials 

(AASHTO) and is widely used among State transportation departments in the United States.
2

common in systems that rely on element-level inspection data. BCIs used in Australia 

(BCN), the United Kingdom (BCI), South Africa (BCI), and Austria (BCI) are the 

examples of weighted combination approaches discussed in this report. 

• The worst-conditioned component approach is common in systems that carry out 

inspections on key bridge components. This method is used to extract the critical defects 

in bridge components. In this approach, the BCI is approximated to the rating of the 

component in the worst condition. Some States also use the worst (lowest) National 

Bridge Inventory (NBI) rating to report bridge conditions at performance dashboards. 

The Michigan Department of Transportation uses the lowest NBI rating in its Bridge 

Condition Forecasting System (BCFS). BCFS helps Michigan with bridge project 

selection decisions. The German and Japanese BCIs are the examples of this approach

and are discussed in this report.

• Qualitative methods do not report the condition of the bridge on a numerical scale. They 

describe a structure as either “Poor,” “Fair,” or “Good,” based on the condition state and 

importance of the elements under investigation. Washington, Florida, and other States use 

NBI condition ratings to classify bridges as “Good,” “Fair,” or “Poor.” The Bridge Health 

Indicator used by Roads and Maritime Services (merger of Roads and Traffic Authority 

and New South Wales Maritime) in Sydney, Australia, is discussed in this report as an 

example to highlight the use of qualitative methods in the assessment of overall 

bridge health.

There are other BHIs that were developed by combining some of the above listed methods. One 

example, no longer used in the United States, is sufficiency ratings (SRs), which combine the 

weighted averaging and the worst condition component approaches. The SR was used in funding 

decisions. Additionally, a risk-based prioritization method currently being tested by the New 

Jersey Department of Transportation (NJDOT) is also discussed in this report. This approach 

combines different performance limit states to calculate the perceived relative risk for 

each bridge.

Although resilience is a very important aspect for management of the bridge network, consensus 

metrics do not currently exist for it. Research programs are actively working on defining metrics 

and acceptable thresholds to address bridge resilience aspects. Some examples of possible 

resilience metrics include the following:

• Regional conditions such as natural hazard zones.

• Geology, seismicity, and geotechnical features of the site (e.g., faulting, landslides, or

liquefaction).

• Toughness and resilience in the event of damage or element failure (e.g., loss of a girder

or fatigue-induced fracture not leading to collapse). 

Although some of these metrics do not currently exist, they may be quantifiable through expert 

elicitation and risk assessment.
3

This report reviews state-of-the-art BCIs being used as one metric to assess performance of 

bridges in the United States and other countries. Table 1 summarizes these indices and their 

calculation approaches.

Table 1. Summary of BHIs and their calculation approaches.

Index Name Calculation Approach

California BHI Ratio based

United Kingdom’s BCI Weighted average

South Africa’s BCI Weighted average

Australia’s BCN Weighted average

Austria’s BCI Weighted average

Finnish Bridge Condition Rating Weighted average

Germany’s BCI Worst conditioned component

Japan’s BCI Worst conditioned component

Australia’s Bridge Health Indicator Qualitative method

Austria’s Qualitative Bridge Rating Qualitative method

Bridge Sufficiency Rating Formulaic combination of 

many parameters

Risk-Based Assessment Framework Formulaic combination of 

risk scores

To facilitate comparison between different bridge condition or health indices, each system is 

reviewed based on the following:

• Computational Approach—The general approach used in calculating the health index 

(e.g., ratio-based, weighted average, worst conditioned component, qualitative, or other 

approach).

• Data Inventory and Condition Rating—Relevant data input for computing the 

condition index (e.g., types of damage observed, severity of damage, extent of damage, 

urgency of damage, etc.).

• Condition Index—Steps used to aggregate the condition information and calculate the 

overall BHI.

• Strengths and Limitations—Discussion of the key strengths and limitations of the 

health index. 

5

CHAPTER 2. RATIO-BASED CONDITION INDEX

COMPUTATIONAL APPROACH OVERVIEW

A ratio-based condition index is frequently used in the United States, Canada, Italy, Japan, and 

other parts of the world.(4–6) It assigns a condition index based on the ratio of the current 

condition to the condition of structure when it was new. 

These indices are mostly adapted from the California BHI, which is a concept originally 

developed by the California Department of Transportation to generate a single-number measure 

of the structural performance of a bridge or a network of bridges. The index assesses the current 

condition of a bridge by aggregating the current condition value of all the elements of the bridge 

and comparing it to the total value of the bridge elements when they were in their best possible 

state. The value of each element is proportional to the quantity of elements in the present 

condition and the economic consequence of the element’s failure. The element’s failure cost

(FC) can be seen as a weight emphasizing the importance of the element to the overall health of 

the bridge. 

DATA INVENTORY AND CONDITION RATINGS

The development of most ratio-based condition indices is based on the following two primary 

sources of data: 

• Element-level bridge condition data.

• Element failure or replacement cost data. 

Element-Level Condition Data

Element-level inspections capture the conditions of more detailed components compared with

the NBI database used by the Federal Highway Administration (FHWA). For instance, instead of 

rating the condition of the whole superstructure (NBI case), an element-level inspection looks at 

the condition of the individual components of the superstructure, such as girders, floor beams, 

pins, hangers, bearings, etc.

Inspectors rate the condition of elements according to the following states and descriptions: 

“Good” (1), “Fair” (2), “Poor” (3), and “Severe” (4). The number of states and descriptions used 

was standardized by the AASHTO Manual for Bridge Element Inspection, which was published 

and adopted in 2013.

(7)

One of the key strengths of element-level inspection is its ability to simultaneously capture the 

severity and extent of deterioration of an element. For example, an inspection of a girder reports

the percentage, or extent, of the girder that is in the different condition states (e.g., 10 percent in 

condition 1, 25 percent in condition 2, and 65 percent in condition 3). 
6

Element Failure or Replacement Cost Data

The cost associated with the failure of an element is estimated from one of the following 

two main sources:

• Agency and User Cost Estimates—The cost to the agency may include operating costs, 

cost of inspection, cost of maintenance, rehabilitation, etc. Examples of user costs include 

estimated costs associated with delays when traffic flow is restricted or diverted, 

increases in vehicle operating costs due to bridge inadequacies, upkeep of detours, etc. 

Also, note that the costs are only for one element. The current BHI method does not 

consider the effect of subordinate elements.

• Element Replacement Cost—This cost is estimated by expert bridge engineers. 

Calculating the California BHI

BHI is based on the premise that a bridge has an initial asset value when it is commissioned. This 

value depreciates due to deterioration caused by traffic loading and environmental effects. 

Interventions through maintenance or rehabilitation improves the value and corresponding 

condition of the bridge asset.(4) The BHI is calculated as the ratio of the aggregate remaining 

value of the bridge elements to the total initial value of the element. The following steps are used 

to calculate BHI.

Step 1

Obtain element-level inspection data from BrM (table 2), with the understanding that an element 

can have portions of it in more than one condition state.

Table 2. Sample element-level inspection data.

Element Unit

Total 

Element 

Quantity

State 1

Q1

State 2

Q2

State 3

Q3

State 4

Q4

State 5

Q5

Element 

FC

Steel 

girder

m 100 40 30 30 0 0 $9,600

Column ea 4 0 0 4 0 0 $7,500

Qn = Quantity of each element in each condition state.

n = Number of condition state for each element.

ea = Each.

Step 2

Calculate a weighting factor (WF) for each of the condition states (figure 1). Table 3 shows an 

example of WFs for various number of condition states. 

Figure 1. Equation. Condition state WF.

WF = Condition State Number − 1

Number of Condition States − 1
7

Table 3. WFs for each condition state.

Number of 

Condition 

States

Condition

State 1 

WF

Condition

State 2 

WF

Condition

State 3 

WF

Condition

State 4 

WF

4 1 0.67 0.33 0

Step 3

Based on current element conditions in step 1, estimate the FC of each element (table 2). The 

two approaches for calculating FC are as follows:

• Element agency FC plus element user FC.

• Element replacement cost multiplied by element WF.

These cost values are established through expert solicitation.

Step 4

Calculate the total element value (TEV) (figure 2) and the current element value (CEV) 

(figure 3).

Figure 2. Equation. TEV.

Figure 3. Equation. CEV.

Step 5

Calculate the BHI as the ratio of the TEV to the CEV (figure 4).

Figure 4. Equation. BHI.

STRENGTHS AND LIMITATIONS

Strengths

The use of element-level inspection data provides a thorough and objective assessment of the 

condition of the bridge. Inspectors are able to capture both the severity and extent of any 

problems that may influence the integrity of the structure. Such information is valuable for 

planning maintenance, repair, and rehabilitation programs. 

The health index is also useful for structural health comparisons and resource allocation for a 

network of bridges. Some State agencies are mostly interested in fixing bridges with the most 

TTTTTT = TTTTTT ∗ FFFF

= �( ii ∗ WW ii) ∗ FFFF

BBBBBB = ∑

∑ TTTTTT

∗ 100
8

severe deficiencies rather than those with clearance and geometric (functional) issues. In such 

cases, the health index can be incorporated into prioritization models used for allocating funds 

for the repair and rehabilitation of bridges with a low health index. 

Limitations

Availability of Element-Level Data

Many agencies, especially at the county level, do not collect element-level data required for 

computing the health index. The recently adopted AASHTO Manual for Bridge Element 

Inspection provides standard guidelines for assessing how good or poor the bridge condition is,

resulting in a more uniform basis for the computed health index.(7)

FC Data

In estimating the FC of an element, since the true cost of an element’s failure is unknown, 

several assumptions and estimations have to be made. This makes the FC uncertain. FCs are 

sometimes related to agency and user costs, which are very difficult to estimate. Different 

agencies will have different FCs. Anything outside the true FC is an estimate and therefore 

uncertain. The variability of FC estimates also increases the difficulty of standardizing the BHI 

across agencies and countries. A replacement cost of one element varies from State to State and 

project to project. Since the replacement cost varies, the health index also becomes variable and 

uncertain. Equal health indices from two different regions might not necessarily mean that the 

two bridges have similar structural condition. Relative structural health comparisons between 

bridges is therefore challenging. 

The Universal Bridge Health Index (UBHI), developed by Sivakumar et al., was intended to 

standardize the use of the index across different States and countries.(9) The UBHI does not 

consider economic value of elements; rather, their physical conditions are used. This helps 

reduce the uncertainties associated with estimating the significance of bridge elements. In place 

of the economic worth or FCs, the UBHI calculates a structural significance factor and material 

vulnerability factor. These two factors, although less uncertain compared with economic cost, are 

still very subjective. The structure significance is found by comparing the role of one element to 

the role of other elements with a range of 1 (least significant) to 4 (most significant). 

Computational Issues

In calculating the health index, only conditions of structural elements of the bridge are 

considered. The bridge’s functional adequacies (service provided by the bridge) such as capacity, 

traffic volume, and clearance issues are ignored. Corporate bridge risk factors such as scour, 

seismic, and fatigue are also not incorporated. Therefore, although the health index provides

management with an indicator of the overall condition of the bridge, it is not a complete measure 

of the value of the agency’s investments.
9

CHAPTER 3. WEIGHTED AVERAGE APPROACHES

COMPUTATIONAL APPROACH OVERVIEW

BCIs calculated by weighted averaging of individual element conditions are the most common

types identified in this report. Their development is based on structural element condition data,

which captures the type, severity, and extent of deteriorations. Also, some indices rely on 

operational data such as traffic volume to capture the service provided by the bridge. The number 

of elements inspected and the type of rating systems adopted may be different from one country 

to the other.

UNITED KINGDOM’S BCI

Just like the California BHI, the United Kingdom’s BCI describes the condition of an element 

based on its condition state and the extent of deterioration. The key difference is that the value of 

the bridge elements’ conditions is based on its contribution to the overall bridge integrity and not 

the cost of the elements’ failure. Instead of calculating the remaining value of the bridge 

elements, a simple score based on engineering judgment is used to assign importance factors to 

each element. Also, the extent of damage is registered in qualitative terms. Table 4 and table 5

provide a description for different categories of damage severity and extent used for calculating 

the United Kingdom’s BCI.

Table 4. Extent descriptions.

(10)

Extent Description

A No significant defect.

B Slight (not more than 5 percent of surface area or length).

C Moderate (5 to 20 percent of surface area or length).

D Wide (20 to 50 percent of surface area or length

E Extensive (more than 50 percent of surface area or length)

Table 5. Severity descriptions.

(10)

Severity Description

1 As-new condition or defect has no significant effect on the element 

(visually or functionally).

2 Early signs of deterioration; minor defect; no reduction in functionality of 

element.

3 Moderate defect/damage; some loss of functionality could be expected.

4 Severe defect/damage; significant loss of functionality and/or element is 

close to failure.

5 The element is non-functional/failed.

Calculating British BCI

The BCI is calculated as follows.

(11)
10

Step 1

Assign an element condition score (ECS) for each element based on its severity and extent of 

deterioration (table 6). For example, an element with a severity of 3 and an extent of C receives a 

score of 3.2. In this approach, higher scores suggest worse conditions.

Table 6. ECS.

(10)

Extent

Severity

1 2 3 4 5

A 1.0 * * * *

B 1.0 2.0 3.0 4.0

5.0 C 1.1 2.1 3.2 4.1

D 1.3 2.3 3.3 4.3

E 1.7 2.7 3.7 4.7

*Non-permissible severity-extent combinations.

Step 2

Assign an element importance factor (EIF) for each element. EIF accounts for the value of the 

element (table 7). 

Table 7. EIF.(10)

Element Importance EIF Value

Very high 2.0

High 1.5

Medium 1.2

Low 1.0

Step 3

Assign an element condition factor (ECF). ECF accounts for an element’s contribution to the 

overall bridge condition. Therefore, ECF of an element is calculated with respect to its 

importance (figure 5 through figure 7); an element with an importance of “very high” has an 

ECF of 0.(10)

Figure 5. Equation. ECF (“high” element importance).

(10)

Figure 6. Equation. ECF (“medium” element importance).

(10)

= 0.3 − [� EE − 1� ∗ 0.3

4 ]

MM = 0.6 − [� EE − 1� ∗ 0.6

4 ]
11

Figure 7. Equation. ECF (“low” element importance).

(10)

Step 4

Calculate the element condition index (ECI) (figure 8).

Figure 8. Equation. ECI.

Step 5

Calculate the overall bridge condition score (BCS). BCS is calculated by a weighted combination 

of all the contributions of each bridge element. The weights are assigned based on the element’s 

importance (figure 9).

Figure 9. Equation. BCS.

Where:

N = Total number of bridge elements for structure.

Step 6

Calculate the BCI (figure 10). The condition of the bridge is based on the BCI value on a scale of 

0 (worst) to 100 (best) (table 8).

Figure 10. Equation. BCI.

Table 8. BCI condition.

BCI Value Condition

90 ≤ BCI ≤ 100 Very good

80 ≤ BCI < 90 Good

65 ≤ BCI < 80 Fair

40 ≤ BCI < 65 Poor

0 ≤ BCI < 40 Very poor

LL = 1.2 − [� EE − 1� ∗ 1.2

4 ]

= EE −

BB = ∑ ( ii ∗ ii) NN

ii=1

∑ ii

NN

ii=1

BB BB = 100 − (2 ∗ {(BB )2 + (6.5 ∗ BB ) − 7.5})
12

SOUTH AFRICA’S BCI

The South African BMS allocates funds and prioritizes maintenance, repair, and rehabilitation 

needs by using an index similar to the British BCI. The BCI is calculated based on data obtained 

from routine structural condition assessments and a bridge importance factor, which is based on 

the average daily traffic (ADT) of the bridge.

Condition Ratings

Condition assessment of structures is performed based on the degree, extent, and relevancy 

(DER) of deterioration by assigning a DER score. The DER rating system identifies defects and 

prioritizes them by evaluating their relative importance to the structural integrity of the bridge.(12)

It is important to note that the ratings are not directly associated with the elements but with the 

distress or damage. Thus, with the DER rating system, an element is assigned a score greater 

than zero only if it has a distress on it.

Each distress identified is assigned a rating from 1 (minor) to 4 (severe) depending on the degree 

(how severe is the defect), extent (how widespread is the defect on the inspected element), and 

relevancy of the damage. The relevancy of the identified damage corresponds to the general 

impact of the defect with regards to structural integrity, serviceability, and safety of the bridge. 

Two defects may look the same and have the same extent, but their impact on the integrity of a 

bridge from a global point of view can be different. Therefore, the relevancy of the distress helps 

the inspectors capture information beyond ordinary visual ratings by assessing the impact of each 

distress on the overall structural integrity of the bridge.(13) The DER rating system is summarized 

in table 9. An urgency category is also assigned based on the DER value, but it is not used to 

determine the BCI.

Table 9. DER rating values.

(12)

Degree Extent Relevancy Urgency

0 None N/A N/A Monitor only

1 Minor Local Minimum Routine

2 Fair > Local Moderate < 5 years

3 Poor < General Major < 2 years

4 Severe General Critical As soon as possible

N/A = Not applicable.

Calculating South African BCI

Each defect on the element being inspected has a condition index (ICj) (figure 11).(12)

Figure 11. Equation. Defect condition index.

Where:

D = Degree of damage.

E = Extent of damage.

jj = 100 ∗ �1 − (DD+ )∗RR

32 �
13

R = Relevancy of damage.

The bridge importance (figure 12) is based on how frequently the bridge is used or traveled in 

the network. Therefore, the overall BCI (figure 13) is computed as the sum of all defect 

condition values for all elements inspected weighted by a bridge importance factor. 

Figure 12. Equation. Bridge importance factor.

Where:

ADTi = ADT for structure i.

n = Number of bridges in the network being evaluated.

Figure 13. Equation. Final bridge condition.

Where:

BCIi = BCI for structure i.

m = Number of inspected elements on structure i.

j = Individual element on structure i.

AUSTRALIA’S BCN

Roads Corporation of Victoria (VicRoads), the roadway agency for Victoria, Australia, uses a 

BCN for relative comparison of the performance, integrity, and durability of bridge structures.(14)

Calculating Australian BCN

BCN is calculated based on a three-level hierarchical framework (figure 14). The first level 

(element level) calculates element-level condition ratings by aggregating condition state 

percentages for each element. At the second level (group level), structural group factors are 

assigned based on the group’s importance to the structure. A structural group consists of a 

number of elements which perform similar functions (e.g., bearings, piers, decks, etc.).

Figure 14. Illustration. Three-level hierarchy for calculating Australian BCN.

BBBB BBBBBB IIIIII IIIIIIII = AA ii

∑ AA ii ii=1

BB BBii = �∑ IIjj jj=1 � ∗ AA ii

∑ AA ii ii=1
14

It is important to note that the level of importance is assigned at the structural group level and not 

at the element level. Combining all the average structural group ratings yields the overall BCN. 

Element Level

Calculate the average condition rating (ACR) for each element (figure 15). Condition state 

numbers are subjective scores represtative of element condition, ranging from 1 to 4, with 1 

being as-built and 4 being poor. Explicit definitions are provided in Rummey and Downling.(14)

Only critical elements are considered in this step.

Figure 15. Equation. ACR for each element.

Group Level (Piers, Decks, Bearings)

Calculate the average group rating (AGR) for each structural groups or categories (figure 16).

Figure 16. Equation. AGR for each structural group/category.

Where:

E = Exposure factor (environment).

Bridge Asset

BCN is calculated in this step (figure 17) using the AGR for bridge element groups.

Figure 17. Equation. BCN.

Where:

Wb = Structural group importance.

Table 10 shows how VicRoads uses the BCN for decisionmaking and prioritization.

Table 10. Decisionmaking with BCN.

BCN Interpretation

Inspection 

Interval (years)

BCN < 30 Free from defects affecting performance and 

durability.

5

30 < BCN < 60 Structure has defect affecting durability. 3

BCN > 60 Structure has defects affecting both performance 

and structural integrity or durability.

2

AA RR = ∑ NN .× %

100

AAAA = ∑[2 × AA + 0.5]

NN . oo EE EE

BB = �[AAAA × WWbb ]
15

AUSTRIA’S BCI

Austria’s BCI is calculated using inspection data from bridge elements. Each element is assigned 

five different ratings based on the following attributes:(15)

• Type of Damage—Rated between 1 and 5 for each of 32 types of damage that can be 

identified. 

• Extent of Damage—Rated between 0 and 1. The extent is not quantified in measured 

size of defects (e.g., length or area).

• Severity or Intensity of Damage—Rated between 0 and 1. 

• Importance of the Structural Components—Rated between 0 and 1 and classified as 

primary, secondary, and other parts. 

• Urgency of Intervention—Rated between 0 and 10 and is dependent on the risk of 

collapse of the structure or element. This attribute is not used in calculating the index. 

Calculating Austrian BCI

The overall bridge condition rating (S) is calculated by weighting the type of distress by the 

square root of the sum of all the above mentioned attributes (figure 18).

Figure 18. Equation. Overall bridge condition rating.

Where:

Gi = Type of damage to element i.

k1i = Extent of damage to element i.

k2i = Severity of damage to element i.

k3i = Importance of component to element i.

FINLAND’S BCI

The BMS used by the Finnish Road Administration (Finnra) uses a condition index based on 

weighted averaging of condition ratings of structural parts.

(12) The weights, assigned by structural 

part, are presented in table 11. Examples of inputs used to calculate the BCI includes damage 

cause, damage location, damage effect on bridge load capacity, and urgency of repair.

Calculating Finnish BCI

BCI, also known as the repair index, is computed for the set of identified defects on the bridge

(see table 12). The bridge is divided into nine structural parts during inspection. The condition of 

each structural part is evaluated on a rating from 0 (very good) to 4 (very poor). Each instance of 

= � ii ∗ �kk1ii + kk2ii + kk3ii

32

=1
16

damage detected during inspection is also rated in terms of its severity and urgency of repair. 

Values for these ratings are shown in table 13 and table 14. 

Table 11. Structural component weights.

Bridge Structural Part Weight

Substructure 0.70

Edge beam 0.20

Superstructure 1.00

Overlay 0.30

Other surface structure 0.50

Railings 0.40

Expansion joints 0.20

Other 0.30

Bridge site 0.30

Table 12. Condition ratings.

Condition Rating Condition Points

0—New 1

1—Good 2

2—Satisfactory 4

3—Poor 7

4—Very Poor 11

Table 13. Repair urgency.

Repair Class Repair Urgency Points

11—Repair during the next 2 years 10

12—Repair during the next 4 years 5

13—Repair in the future 1

Table 14. Damage severity.

Damage Class Damage Severity Points

1—Mild 1

2—Moderate 2

3—Serious 4

4—Very Serious 7
17

The repair index is computed for all identified defects (figure 19). The equation maximizes the 

worst defects and minimizes all other defects by a factor k, which has a default value of 0.2.

Figure 19. Equation. Repair index.

Where:

KTI = Repair index.

Wt = Weight assigned to structural part.

i = Index representing the worst defect on a given structural part.

C = Condition of structural part.

U = Urgency of the repair needed for structural part.

D = Severity of damage to structural part.

k = WF for other defects apart from the worst defect.

j = Indices representing the rest of the defects on a given structural part.

STRENGTHS AND LIMITATIONS

Strengths

The weighted averaging condition indices capture the degree, severity, and importance of 

every instance of damage identified during the inspection process, which helps provide a 

comprehensive picture of the condition of the bridge. Also, the approach is suitable for planning 

for bridge maintenance and rehabilitation activities because the overall index combines all 

defects identified at the element level. These indices provide a consistent framework within an 

agency, and engineering judgment has been incorporated by assigning categories rather than 

rigid numerical scores.

Limitations

The health index only captures conditions of structural elements of the bridge. Although the 

bridge’s functional adequacies (service provided by the bridge) such as capacity, traffic volume,

and clearance issues are considered during maintenance prioritization and fund allocation, there 

is no index in the weighted average category integrating both structural condition and functional 

information. Finnra overcomes this challenge by using a rehabilitation index that combines 

structural condition information with some functional information.(12)

With the exception of the Australian BCN and Finnra’s repair index, most of the weighted 

combination health indices assign weights (significance level) at the element level. This is

challenging because it is very difficult to assess the impact of the condition of an element on the 

overall bridge structure. Estimating the importance of a structural group (consisting of a number 

of elements with similar primary functions) is more practical. 

KK = max(WW ii ∗ ii ∗ UUii ∗ DDii) + kk�(WW jj ∗ jj ∗ UUjj ∗ DDjj )

19

CHAPTER 4. WORST-CONDITIONED COMPONENT APPROACHES

COMPUTATIONAL APPROACH OVERVIEW

The worst-conditioned approach is driven by bridge component condition data that capture the 

severity and extent of identified forms of deterioration. The approach captures information about

the critical defects in bridge components. Not all damage is factored into the calculation of 

overall BCI. The condition rating of the whole structure corresponds to the state of the worst 

conditioned components. The component in the worst condition is related to the individual 

damage with the worst rating based on its severity and frequency of occurrence among other 

components of the structure. The number of components contributing to the index and the type of 

rating system adopted may be different from one country to the other.

GERMANY’S BCI

The German BCI uses a hierarchical approach to assess the overall health of a structure. At the 

lowest level, an index is assigned to each individual damage identified. The next level involves 

calculating a condition index for predefined groups of structural components (i.e., piers, 

bearings, etc.) followed by a final level that computes the overall BCI. 

Each instance of damage detected during inspection is rated on a five-level scale in terms of its 

effect on the bridge’s structural stability (table 15), traffic safety (table 16), and the bridge’s 

durability (table 17). The extent of damage is not quantified by measured length or area. It is 

described qualitatively as either small, medium, or large. From this information, a decimal 

condition index (table 18) ranging from 1.0 (very good condition) to 4.0 (insufficient condition) 

is assigned for each damage. 

Table 15. Damage ratings for structural stability.

(3)

Assessment Description

0 Defects have no effect on structural stability of elements or 

overall structure.

1 Defects affect stability of structure elements but not the overall 

structure.

2 Defects affect stability of structure elements and have little 

effect on stability of overall structure. 

3 The effect of defects on stability of structural elements and the 

overall structure is beyond permissible tolerance.

4 The structural stability of structural elements and the structure

itself no longer exists. 
20

Table 16. Damage ratings for traffic safety.

(3)

Assessment Description

0 Defects have no effect on traffic safety.

1 Defects affect traffic safety only slightly.

2 Defects may impair traffic safety. 

3 Defects affect traffic safety.

4 Traffic safety is no longer given due to defects. 

Table 17. Damage ratings for durability.

(3)

Assessment Description

0 Defects have no effect on durability.

1 Defects affect durability of structure elements but not the 

durability of the overall structure.

2 Defects affect durability of the structure elements and, in the 

long term, can affect the overall structure.

3 Defects affect durability of the structure elements and, in the 

medium term, can affect the overall structure.

4 The durability of both the structure element and the overall 

structure is no longer given due to the defects. 
21

Table 18. Damage condition ratings.

(3)

Condition 

Rating Description

1.0–1.4 • Very good structural condition. 

• The stability, traffic safety, and durability of the structure 

is assured.

1.5–1.9 • Good structure condition.

• Stability and safety of structure is assured.

• Durability might be impaired slightly in the long term.

2.0–2.4 • Temporarily satisfactory structural condition.

• Stability and safety of structure is assured.

• The durability of the structure might be impaired 

considerably in the long term. 

2.5–2.9 • Unsatisfactory structural condition.

• Stability of structure is assured.

• Traffic safety can be impaired.

• The durability of the structure might be impaired 

considerably in the long term.

3.0–3.4 • Critical structural condition.

• Traffic safety is affected.

• Structure is not durable.

• Immediate repair is needed.

3.5–4.0 • Inadequate structural condition.

• Traffic safety is not adequate.

• Structure is not durable.

• Immediate repair or rehabilitation is needed.

Calculating German BCI 

The overall condition of the bridge corresponds to the rating of the worst component rather than 

the aggregate component conditions. 

Damage Index

Each component is surveyed for damage or deterioration. For each individual occurrence 

of damage, an index (Zi) is calculated based on its effect on traffic safety, stability, and

durability. The condition index is supplemented with the extent of the identified damage ( 1) 

and assigned a value (table 19). 

Table 19. Identified damage values.

1 Value Damage Extent

-0.1 Small

0.0 Medium

+0.1 Large

∆

∆
22

Each component group (CG) consists of damage ratings for each individual occurrence

(figure 20).

Figure 20. Equation. Component group.

Next, a component group condition index is calculated.

Component Group-Level Condition Index

The index at the component group level is equivalent to the maximum ratings assigned to 

damage at the subcomponent level. The number of occurrences of the damage identified within 

the component group ( 2) is accounted for in calculating the component group condition 

index (ZCG_i) (figure 21). 

Figure 21. Equation. Component group condition index.

For a substructure component group, 2 is assigned a value according to table 20.

Table 20. Values of 2 for substructure component groups.

2 Value

Number of 

Damage 

Occurrences (n)

-0.1 n < 5

0.0 5 ≤ n ≥ 15

+0.1 n > 15

For all other components groups, 2 is assigned a value according to table 21.

Table 21. Values of 2 or other component groups.

∆2 Value Number of Damage Occurrences

-0.1 n < 3

0.0 3 ≤ n ≥ 5

+0.1 n > 5

Structure-Level Index

The overall bridge condition index (Zges) (figure 22) corresponds to the maximum rating at the 

component group level, taking into consideration the extent of damage to other component 

groups. The extent of damage to other component groups ( 3) is assigned a value based on the 

number of damaged component groups (table 22).

Figure 22. Equation. German BCI.

= �ZZ1, ZZ2, ZZ3,......,ZZNN�

∆

ZZ _1 = max{ZZii} + ∆2

∆

∆

∆

∆

∆

∆

ZZ = max{ZZ } + Δ3
23

Table 22. Values of 3.

3 Value Number of Damaged Component Groups

-0.1 1 to 3

0.0 4 to 5

+0.1 more than 5

JAPAN’S BCI

The Japan BMS uses visual inspection to assess the condition of bridge components at the 

element level.(16) Each instance of damage is described based on the type and severity of 

deterioration alone. A deficiency (or condition) rating is established for each identified instance 

of damage. During inspection, each element is divided into units, and the condition of the 

structure is assessed by aggregation of units.

Japan’s BCI is slightly different from that of Germany. It calculates the overall BCI by 

aggregating worst defects (in terms of severity) detected for all components, whereas the German 

BCI selects the worst component as the condition of the overall bridge, with no aggregation 

required. Also, Japan’s BCI calculation does not directly incorporate the extent of damage. 

Calculating Japanese BCI

Step 1

Assign deficiency ratings (table 23) for each defect within each structural component of the 

bridge.

Table 23. List of deficiency ratings.

(16)

Deficiency Rating Description

I Serious damage. There is a possibility of danger to traffic.

II Damage in a large area. Detailed investigation is required.

III Damage. Follow-up investigation is required.

IV Slight damage. Inspection data are recorded.

OK No damage.

Step 2

Calculate a demerit rating (d) corresponding to the deficiency rating for each type of defect

(figure 23). Demerit rating for distress with worst deficiency ratings (dI) is assigned and not 

calculated. The remaining demerit ratings are calculated as follows:

∆

∆
24

Figure 23. Equation. Demerit ratings.

Where: 

= Reducing ratio (table 24) corresponding to each deficiency rating.

Table 24. Deficiency ratings and reducing ratios.

(16)

Deficiency Rating Reducing Ratio

I 1

II 0.5

III 0.2

IV 0.05

OK 0

Step 3

Determine the value of the demerit rating for each structural component by taking the maximum 

demerit rating for all defects with that component group. 

Step 4

Calculate the overall bridge condition rating by adding all defective ratings for the structural 

groups and subtracting it from 100. 

STRENGTHS AND LIMITATIONS

Strengths

Worst-conditioned component approaches are useful for assessing the vulnerability of a bridge 

in case of disasters or extreme events. At the network level, the approach can be used for 

identifying high-risk bridges. This is possible because the approach correlates the condition of 

the bridge to the weakest link in the structure. 

Limitations

This approach does not give a full picture of how deterioration is spread over the bridge. The 

total amount of defects (not the worst defect) is required for planning bridge maintenance 

repair and rehabilitation projects. Using this approach with weighted averaging methods is

more helpful.

= ∗∝

= ∗∝

= ∗∝

OO = 0

∝
25

CHAPTER 5. QUALITATIVE METHODS

COMPUTATIONAL APPROACH OVERVIEW

Qualitative methods provide a direct, descriptive indication of the bridge condition rather than 

using a numeric scale. The index is assigned after extensive assessment of the condition of 

bridge elements using element-level inspection. A typical example of qualitative health index is 

the Bridge Health Indicator developed by Roads and Maritime Services in Sydney, Australia. 

AUSTRALIA’S BRIDGE HEALTH INDICATOR

The bridge health indicator is used by Roads and Maritime Services for identifying bridges that 

need maintenance, repair, or rehabilitation, but it is not used for prioritizing projects. The bridge 

health indicator does not report the condition of a bridge on a numerical scale. It describes a 

structure as having an indicator of “Poor,” “Fair,” or “Good” based on the condition state and 

importance of the element under investigation. The element’s importance is a reflection of the 

relative significance of the element to the overall performance of the structure. The significance 

or importance of an element is ranked as high, medium, or low. The element importance 

rankings are based on an expert determination of the proportion of similar elements that, if lost, 

will result in a collapse.

(17) Table 25 describes how the overall bridge health is assessed based on 

the condition and importance of the elements. 

Table 25. Bridge condition description based on element importance and condition states.

Bridge 

Health

Bridge Element Importance

High Medium Low

Poor Percent in condition 

state 5 > 10

Percent in condition 

state 4 > 40

Percent in condition 

state 5 > 25

Percent in condition 

state 4 > 50

Percent in condition 

state 5 > 50

Percent in condition 

state 4 > 70

Fair 10 ≥ Percent in condition 

state 5 > 0

40 ≥ Percent in condition 

state 4 > 0

25 ≥ Percent in 

condition state 5 > 0

50 ≥ Percent in 

condition state 4 > 0

50 ≥ Percent in 

condition state 5 > 0

70 ≥ Percent in 

condition state 4 > 0

Good 0 percent in 

condition 4 or 5

0 percent in 

condition 4 or 5

0 percent in 

condition 4 or 5

As an example, an element of high importance with 15 percent of the element in condition state 5 

is considered to be in “Poor” condition. An element of low importance with 50 percent in 

condition state 4 is considered to be in “Fair” condition.

AUSTRIA’S QUALITATIVE BRIDGE RATING

Although Austria has a BCI, most of the relevant infrastructure administrations do not use this 

calculation anymore but use simple ratings between 1 (no/minor damage) and 5 (critical 

condition).
26

Following the Austrian guideline for bridge inspections, the total rating of a bridge is based on 

the ratings of the bridge elements.(15) Each element is assigned a condition rating, ranging from 1 

to 5 (table 26).

Table 26. Description of condition ratings for bridge elements in Austria’s qualitative 

approach.

Rating Description

1 No problems, minor problems; load-bearing capacity, operability, and durability not 

limited; no maintenance required.

2 Minor problems; load-bearing capacity and operability not limited; operability and 

durability will be limited if defects are not removed in the long-term; no restriction 

of use.

3 Moderate problems; indication of limited operability and durability; maintenance 

required in the medium term (within 6 years).

4 Severe problems; load-bearing capacity not yet limited but operability and durability 

already limited; maintenance within 3 years (short term) to reestablish regular use.

5 Critical condition; load-bearing capacity and operability limited; immediate initiation 

of repair, restriction of use.

On the basis of the bridge element ratings, the total rating of a bridge is also assigned a number 

from 1 to 5. The following factors are crucial for this classification:

• Extent/severity of damage.

• Limitation of load-bearing capacity, operability, and durability.

• Urgency of intervention.

STRENGTHS AND LIMITATIONS

Strengths

This approach is mainly used for general assessment of the bridge condition and identifying 

bridges that need maintenance. Qualitative methods rely on element-level inspection data and are

able to provide a more objective assessment of the condition of structural elements by capturing 

both severity and extent of damages. 

Limitations

This approach cannot be used effectively for prioritizing and planning rehabilitation and 

maintenance programs because it does not provide a quantitative scale for ranking bridges in a 

network. For example, many bridges may be rated as being in “Poor” condition with no 

particular ranking regarding which ones are in dire need of repair or replacement compared with

others when only a few of them could be preserved or replaced due to budget constraints.
27

CHAPTER 6. OTHER METHODS

There are other BCIs that cannot be categorized into any one of the methods described in

chapter 5. These indices use multiple approaches to calculate the overall BHI. 

BRIDGE SR 

The bridge SR was previously used in the United States for evaluating factors, indicating a 

bridge’s sufficiency to remain in service, but was superseded as a result of the recent Moving 

Ahead for Progress in the 21st Century Act (MAP-21) legislation. The inspector rated each of 

the key components of the bridge by selecting a deterioration that best described the general 

condition of the component being inspected. The overall bridge rating was obtained by a 

weighted combination of the structural condition information and functional information. The SR

approach was therefore an extension of the weighted averaging approach.

Data Inventory and Condition Rating

Bridge SRs were calculated by using data from NBI, which is a comprehensive database 

compiled by FHWA of all bridges with span lengths greater than or equal to 6.1 m on public 

roads. The database contains a collection of bridge information data items such as bridge 

identification or location, bridge type and specifications, operational conditions (i.e., age, 

average daily traffic, bypass, and detour length), bridge geometric or functional data 

(i.e., structure lanes, shoulder width, etc.), and bridge structural condition data (i.e., rating 

of deck, superstructure, and substructure). The SR was calculated using bridge functional, 

operational, and condition information.

Functional Information

Functional data provided an assessment of the level of service provided by the bridge. Examples 

of functional data in NBI include number of lanes, shoulder width, vertical under clearance 

(height of the bridge), etc. These data were also used by FHWA to rate or classify the service 

provided by a bridge. Bridges not meeting minimum clearance values (i.e., narrow lanes, narrow 

shoulders, inadequate vertical under clearance, etc.) were classified as functionally obsolete. A 

functionally obsolete bridge contained features below established limits. However, they may 

have been structurally sound and perfectly safe. In calculating SR, the bridge’s serviceability and 

functional obsolescence contributed a maximum of 30 percent to the SR rating.

Operational Condition Information

The operational conditions of a bridge were based on the evaluation of factors such as average 

daily traffic, bypass, detour length, and highway designation. Operational conditions contributed

a maximum of 15 percent to the overall SR.

Condition Information

The NBI database describes the structural condition of only key components of a bridge: the 

deck, the superstructure, and the substructure. 
28

The bridge deck, which directly carries traffic, is inspected for defects such as cracking, scaling, 

spalling (for concrete decks), broken welds, broken girds, and section loss (for steel grid decks). 

Timber decks are inspected for splitting, crushing, fastener failure, etc. The condition of the 

bridge deck is rated based on the defects identified and in accordance with the general condition 

ratings in table 27. The superstructure that supports the deck and connects one substructure 

element to another is inspected for signs of distress, which may include cracking, deterioration, 

section loss, malfunction, and misalignment of bearings. The substructure supports the 

superstructure and distributes all bridge loads to bridge foundations. The substructure is 

inspected for visible signs of distress, including evidence of cracking, section loss, settlement, 

misalignment, scour, collision damage, and corrosion.

Table 27. NBI condition ratings.

(18)

Rating Description

9 Excellent condition.

8 Very good condition. No problems noted.

7 Good condition. Some minor problems.

6 Satisfactory condition. Structural elements show some minor 

deterioration.

5 Fair fondition. 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 and/or deterioration of primary 

structural elements. 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 shear cracks in concrete may be 

present or scour may have removed substructure support. Unless 

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 vertical or 

horizontal movement affecting structure stability. Bridge is closed to 

traffic, but corrective action may put it back in light service.

0 Failed condition. Out of service and beyond corrective action.

The structural condition of a bridge’s key components (deck, superstructure, and substructure) is 

used to assess whether it is structurally deficient (NBI rating of 4 or less for deck, superstructure,

or substructure). FHWA classifies a bridge as structurally deficient to indicate that the physical 

conditions of the bridge’s primary load-carrying elements have deteriorated. A “structurally 

deficient” bridge is not necessarily unsafe, but the owner may need to spend significant amounts 

on repair and maintenance to the keep the bridge in service, and the bridge would eventually 

require major rehabilitation or replacement to address the underlying deficiency. 
29

Calculating SR

In calculating SR, the bridge’s structural adequacy and safety together with the inventory loading 

contribute a maximum of 55 percent to the total rating.

The calculated SR (figure 24) is a function of four factors: structural adequacy and safety (A), 

serviceability and functional obsolescence (B), essentiality for public use (C), and special 

reductions (D), which is a maximum of 13 percent of the total rating. Elements considered 

include the detour length, traffic safety features, and main structure type. 

Figure 24. Equation. SR.

Uses of SR

Funding Eligibility

Previously, FHWA used SRs with a status flag, indicating whether a bridge is structurally 

deficient or functionally obsolete to decide on its eligibility for funding. A structurally deficient 

(or functionally obsolete) bridge with an SR less than 50 qualified for replacement, whereas a 

structurally deficient (or functionally obsolete) bridge with an SR greater than 50 but less than 80 

qualified for rehabilitation.

RISK-BASED PRIORITIZATION FOR BRIDGES

Moon et al. proposed a risk-based method for prioritization of bridge repair and replacement 

projects in a network. This method provides the basis for a bridge prioritization tool being tested

by NJDOT. Although this is a risk-based framework, because risk and resilience are critical 

components of bridge health and performance, this method is included in this synthesis to 

address that aspect of bridge health.(19)

The objective of this proposed method is to provide a risk-based approach that transportation 

authorities can use as a more transparent and objective approach to bridge evaluation and project 

prioritization. While the method appears qualitative in nature, it has distinct advantages over 

many current approaches. This approach defines risk as a product of hazards, vulnerabilities, and 

exposures and therefore explicitly recognizes key performance limit states. In addition, it 

incorporates the uncertainties associated with various assessment techniques, provides flexibility 

for their implementation, and provides a means to capture (in a useable format) expert 

knowledge and heuristics from top bridge engineers.

Definition of Risk

The proposed bridge assessment methodology is based on the concept of relative risk, which 

extends the reliability-based assessment approach to explicitly consider the consequences of not 

performing (in this definition called exposure). The inclusion of consequences is a necessary 

consideration for rational decisionmaking, and it is therefore imperative that consequences be 

included within the assessment procedure. The proposed framework takes into consideration a 

= AA + BB + − DD
30

more partitioned definition for perceived relative risk (referred to as “risk” in this report) as a 

combination of hazard, vulnerability, exposure, and an uncertainty premium (figure 25). 

Figure 25. Equation. Perceived relative risk.

Where:

Hazard = Probability of a hazard occurring.

Vulnerability = Probability of failure (to perform adequately) given hazard.

Exposure = Consequences associated with a failure to perform adequately.

Uncertainty Premium = A factor to account for the level of uncertainty associated with the 

selected assessment approach, including the quality control measures employed.

Table 28 outlines some proposed hazards, vulnerabilities, and exposures for the four 

performance limit states to be considered by the proposed risk-based assessment approach.

Perceiced Relative Risk (H) = (Hazard) (Vulnerability) (Exposure) (Uncertainty Premium)
31

Table 28. Summary of relevant performance limit states, hazards, vulnerabilities, and 

exposures for bridges.

(19)

Performance 

Limit States Hazards Vulnerabilities Exposures

Safety—

geotechnical/ 

hydraulic

• Flood plain.

• Seismic design 

category.

• Marine traffic.

• Storm surge 

category.

• Underwater 

substructure 

flowrate.

• Foundation bearing 

conditions.

• Pier protection 

standards.

• Scour critical.

• Evidence of 

substructure 

settlement.

• Superstructure 

above/below flood 

level.

• Replacement 

cost.

• Coastal 

evacuation 

route.

• Distance of 

detour route.

• Strategic 

Highway 

Network route.

• Utility 

disruption.

Safety—

structural

• ADTT.

• Seismic design 

category.

• Structural assembly 

classification.

• Fatigue details.

• History of 

displacements and 

vibrations.

• Evidence of structural 

damage.

• Spanned roadway 

functional 

classification.

• Fracture critical details.

• Exposed prestressing 

strands.

• Rocker bearings.

Loss of life.
32

Performance 

Limit States Hazards Vulnerabilities Exposures

Serviceability

and durability

• ADTT of spanned 

roadways.

• Average annual 

snowfall.

• Use of deicing salts.

• Freeze-thaw cycle.

• Proximity to coast.

• History of vehicular 

collisions.

• Water penetration/

corrosion.

• Bearing conditions.

• Expansion joint 

condition.

• Condition rating of 

approach.

• Condition rating of 

superstructure.

• Condition rating of 

substructure.

• Condition rating of 

deck.

• Under clearance of 

spanned roadways.

Maintenance 

costs.

Operations • History of fatal 

accidents.

• Utilities on 

structure.

• Lane width.

• Line striping condition.

• Traffic safety feature 

adequacy.

• Breakdown 

lanes/shoulders.

• Percentage of legal 

truck weight posted.

History of 

congestion.

ADTT = Average daily truck traffic.

The framework scales the calculated risk using the Department of Homeland Security’s fivelevel risk scale (figure 26) in which “I” represents low risk level, and “V” represents severe risk 

level. This scale is easy to understand for both engineers and the general public.

Figure 26. Chart. Risk scale for risk-based prioritization framework. RISK LEVEL 

►

V

SEVERE RISK BRIDGES

IV

HIGH RISK BRIDGES

III

SIGNIFICANT RISK BRIDGES

II

GENERAL RISK BRIDGES

I

LOW RISK BRIDGES
33

Risk-Based Assessment Framework

Moon et al. stress that the proposed framework is very rudimentary and needs to be refined

based on expert elicitation and input from the many relevant professional organizations and

committees.

(19) While this framework has subjective components (due to the current lack of 

quantitative and objective data), as bridge performance research programs such as the LTBP 

Program expand their field data collection efforts, it is expected that this framework will become 

increasingly objective in nature by using data-driven inputs.

(19)

Figure 27 shows a flowchart for the proposed risk-based prioritization. In this approach, the level 

of risk assessment is defined first, which identifies the acceptable uncertainty premium. After 

this definition, the estimation of relative risk is done by determining the hazard, vulnerability,

and exposure of the bridge. The risk level is then calculated, which helps informed 

decisionmaking and budget allocation. 

Figure 27. Flowchart. Proposed risk-based assessment framework.

(19)

Uncertainty premiums associated with different levels of risk assessment are listed in table 29. 

The major deciding factor in the uncertainty premium is the level at which the risk is computed, 

whether at an aggregate level or divided up into individual risks. Although computing the risk in 

an aggregate level is more conservative and time efficient, it sometimes overestimates the actual 

risk drastically. In these cases, calculating a more realistic risk based on individual hazards as an 

accurate risk assessment can be worthwhile. The assessment levels reflect the specific 

approaches and technologies employed. More advanced analytical and experimental technologies 

are becoming available that can help users better understand the conditions of a structure and 

reduce the uncertainty premium. Also, a wide range of successful quality assurance programs 

have been developed. To recognize their influence and benefits, assessment levels that take 

advantage of these developments will have a lower uncertainty premium associated with them. 

Table 30 through table 32 show how hazard, vulnerability, and exposure may be quantified for 

levels 1 and 2 assessments. In this case, the risks are groups in four categories: safety—
34

geotechnical/hydraulic; safety—structural; serviceability, durability, and maintenance; and 

operational and functional. For each of these categories, the hazard, vulnerability, and exposure 

are assigned a value of 1 through 3 based on location, structural and operational attributes, age, 

etc. The risk levels are then be calculated as discussed earlier in this section. Table 33 lists the 

preliminary risk levels.

Table 29. Risk assessment levels.

(19)

Level Example Approaches Resolution

Quality 

Assurance

Uncertainty 

Premium

1 Visual Inspection, Document 

Review

Aggregate 

Risks

Minimum

Standards

2.5

2 Visual Inspection, Document 

Review

Aggregate 

Risks

Best 

Practices

2.0

3 Visual Inspection, Document 

Review, Analytical Techniques

Individual 

Risks

Minimum

Standards

1.5

4 Visual Inspection, Document

Review, Analytical Techniques

Individual 

Risks

Best 

Practices

1.25

5 Visual Inspection, Document

Review, Analytical and

NDE Techniques

Individual 

Risks

Best 

Practices

1.0

NDE = Nondestructive evaluation.

Table 30. Preliminary hazard values for level 1 and 2 risk assessments.

(19)

Hazards

Considered

Hazard Values

1 2 3

Safety—

geo/

hydraulic

Scour,

debris and ice,

vessel collision,

seismic—

liquefaction,

settlement,

flood

Outside of a 500-year 

flood plain

Outside of a 100-year 

flood plain

Within of a 100-year 

flood plain

Seismic design 

category A

Seismic design 

categories B and C

Seismic design categories 

D, E, and F

Over a non-navigable 

channel

Navigable channel for

mid-sized vessels

Navigable channel for

large vessels

Located more than

804 km from coast

Located more than

80.4 km from coast

Located within

80.4 km from coast

No potential for scour A rating of NBI item 113 

(scour) of 7, 5, or 4 Not applicable

No records of significant 

earthquake, floods, or

storm surge

Records of moderate 

earthquake, floods, or 

storm surge

Observed drift and debris 

at piers/abutment history 

of ice flows in waterway
35

Hazards

Considered

Hazard Values

1 2 3

Safety—structural

Seismic,

fatigue,

vehicle 

collision,

overload,

fire

Seismic design category A Seismic design 

categories B and C

Seismic design categories

D, E, and F

ADTT less than 500 ADT less than 10,000 ADT more than 10,000

Not spanning over a 

roadway

Spanning over a roadway 

with ADTT less than 

1,000

Spanning over a roadway 

with ADTT more than 

1,000/spanning a rail line

Located more than

16 km from heavy industry

Located more than 

16 km from heavy 

industry

Located less than 16 km

from heavy industry

No history of overloads, 

collision, or earthquake

Limited number of 

overloads or collision or 

minor earthquakes

History of overloads, 

collision, or severe 

earthquake

Serviceability, 

durability,

and maintenance

No routine use of deicing 

salts

Moderate usage of 

deicing salts

High usage of deicing 

salts

Located more than 100 mi

from the coast

Located more than 25 mi

from the coast

Located less than 25 mi

from the coast

Low number of freezethaw cyclesModerate number of 

freeze-thaw cycles

Moderate number of 

freeze-thaw cycles

No history of overloads History of isolated 

overloads

History of repeated 

overloads and permits

Operational and

functional

ADTT less than 1,000 and 

ADT less than 10,000

ADTT less than 10,000 

and ADT less than 

50,000

ADTT more than 10,000 

and ADT more than 

50,000

No history of fatal 

accidents

History of isolated fatal 

accidents

History of repeated fatal 

accidents

No history of congestion History of moderate 

congestion

History of high 

congestion

Table 31. Preliminary vulnerability values for level 1 and 2 risk assessment.

(19)

Vulnerabilities 

Considered

Vulnerability Values

1 2 3

Safety—

geo/hydraulic

Founded on deep foundations 

or bedrock

Founded on shallow 

foundations on cohesive soil

Founded on shallow 

foundations or noncohesive 

soil

No history and no evidence of 

scour or settlement

Evidence of minor scour/ 

undermining during 

past/present underwater 

inspections

Evidence of moderate to 

significant scour/ 

undermining during 

past/present underwater 

inspections

Meets current pier impact and 

scour protection standards

Pier protection system in 

good condition

Pier protection system 

missing or in poor 

condition
36

Vulnerabilities 

Considered

Vulnerability Values

1 2 3

Superstructure above

100-year flood level

Superstructure above

100-year flood level

Superstructure below

100-year flood level

No tilt of substructure 

elements

Minor tilt of substructure 

elements

Significant tilt of 

substructure elements

Safety—

structural

Meets all current design specs Does not meet all current 

design specs, but most of 

them

Noncomposite construction

Structure displays 

bi-directional redundancy

Simply supported constructed 

with transverse distribution 

capabilities

Simply supported 

construction with minimal 

transverse distribution 

capabilities

20 years or less since 

construction or major renewal

50 years or less since 

construction or major 

renewal

50 years or more since 

construction or major 

renewal

A and B fatigue details C and D fatigue details E and E' fatigue details

Elastomeric bearings Steel bearings Rocker bearings, intrinsic 

force dependency, exposed 

prestressing strands, and 

pin and hanger details

No evidence of structural 

damage

Minor evidence of structural 

damage within the critical 

load path

Evidence of structural 

damage within the critical 

load path

Clearance more than 15.2 cm

of current standard

Clearance within 15.2 cm of 

current standard

Clearance below current 

standards

No history of excessive 

displacements or vibrations

History of significant 

displacements or vibrations

History of excessive 

displacements or vibrations

Substructure elements plumb Substructure elements within 

10 percent of plumb

Substructure elements more 

than 10 percent of plumb
37

Vulnerabilities 

Considered

Vulnerability Values

1 2 3

Serviceability, 

durability, and 

maintenance

No visible cracks Minor local cracking Extensive cracking and 

spalling

No evidence of reinforcement 

corrosion

Some evidence of 

reinforcement and structural 

steel corrosion

Evidence of widespread 

reinforcement and 

structural steel corrosion

Paint in good condition Paint in moderate condition Paint in poor condition

Elastomeric bearing Steel bearing Frozen bearings and 

exposed prestressing 

strands

Joints in good operating 

condition

Joints with minor evidence of 

leaking

Failed expansion joints

Approach does not display 

rutting

Approach displays minor 

rutting

Approach displays 

significant rutting

Scuppers are less than 

10 percent clogged

Scuppers are between 10 and 

50 percent clogged

Scuppers are between 50

and 100 percent clogged

Operational and

functional

Roadway approach alignment 

and bridge geometry up to 

current standards

Lane width within 0.3 m of 

current standards

Lane width more than 

0.3 m less than current 

standards

Guard rail and road paint in 

good condition

Guard rail and road paint in 

fair condition

Guard rail and road paint in 

poor condition

Not posted Posted for more than 

90 percent of legal truck 

weight

Posted for less than 

90 percent of legal truck 

load

Good ride quality of deck Moderate ride quality of deck Poor ride quality of deck

Breakdown lane/shoulders Breakdown lane/ shoulders 

not present

Breakdown lane/shoulders 

not present

No rutting of pavement Minor rutting of pavement Significant rutting of 

pavement
38

Table 32. Preliminary exposure levels for level 1 and 2 risk assessments.

(19)

Exposure Considered

Exposure Values

1 2 3

Safety—geo/hydraulic

Safety—structural

ADT less than 10,000 ADT less than 50,000 ADT more than 50,000

Replacement cost

less than $2 million

Replacement cost

less than $10 million

Replacement cost

more than $10 million

Not on a critical route 

(life line, evacuation 

route, etc.)

Not on a critical, 

nonredundant route 

(life line, evacuation 

route, etc.)

On a critical, 

nonredundant route 

(life line, evacuation 

route, etc.)

Detour route less than 

8 km

Detour route less than 

16 km

Detour route more than 

16 km

Serviceability, 

durability, and 

maintenance

Low maintenance costs High maintenance and 

repair costs

N/A

ADT less than 50,000 ADT more than 50,000

Operational and

functional

No history of congestion

Average peak hour 

delays of more than 

10 min

N/A

ADT less than 25,000 ADT more than 25,000

ADTT less than 10,000 ADTT more than 10,000

N/A = Not applicable.

Table 33. Preliminary risk levels.

(19)

Risk Level

Threshold Risk 

Values

Level V: Severe risk bridges > 40

Level IV: High risk bridges 30–40

Level III: Significant risk bridges 20–30

Level II: General risk bridges 10–20

Level I: Low risk bridges < 10

In order to translate risk levels into appropriate actions, assessment techniques, and required 

intervals for assessments, a set of minimum requirements and optional assessment programs is 

needed. A preliminary estimate of this relationship is shown in table 34.
39

Table 34. Preliminary assessment programs per risk level.

(19)

Risk Level Mandatory Option 1 Option 2

Severe Level 3 / 1 Year Level 4 / 18 months Level 5 / 2 years

High Level 2 / 1 Year Level 4 / 2 years Level 5 / 3 years

Elevated Level 2 / 2 years Level 4 / 3 years Level 5 / 4 years

Guarded Level 1 / 2 years Level 4 / 4 years Level 5 / 6 years

Low Level 1 / 2 years Level 4 / 4 years Level 5 / 6 years

Note that the acceptable risk level that triggers more refined risk assessment and also relative 

quantitative values for uncertainty need to be calibrated based on case studies and expertise of 

experienced engineers. 

Strengths and Limitations

Strengths

The proposed approach recognizes the diverse set of performance limit states relevant to 

management decisions and can readily be incorporated within risk-based decision-support 

tools. While this framework remains highly qualitative and subjective in nature, it has the 

advantage of requiring very limited changes on the actual practice of bridge inspections, and it 

can be implemented for most bridges using current inspection data and other publicly available 

data sources.

This approach not only provides decisionmakers with a more complete picture of the uncertainty 

associated with various assessment procedures, but it also promotes the use of more reliable 

approaches while still providing States some freedom regarding implementation depending upon 

their individual priorities and concerns.

Limitations

Although calculating actual risks assocated with bridges is ideal, it is not possible in practice. For 

this reason, performance-based risk methods yield a perceived risk, which is valuable in a 

relative sense.

The proposed framework adopts key performance limit states (safety; durability, serviceability,

and maintenance; and operations and functionality), including State or regional costs associated 

with operation, evaluation, maintenance, and repair. Bridge performance is a more complex 

concept, and performance of a bridge may cover other limit states that are not fully known. It is 

expected that as this assessment procedure matures and the findings of the LTBP Program are 

released, additional performance limit states may be included, and some of these performance 

limit states may be subdivided to allow for a higher resolution assessment.

41

CHAPTER 7. CONCLUSIONS

This synthesis discussed state-of-the-art bridge condition or health indices being used to assess 

performance of bridges in the United States and other countries. Current methods for developing 

condition or health indices were grouped into four different approaches based on the 

computational methods used. A discussion on each approach covered the data required for 

computing the index and the strengths and limitations of the approach.

The majority of health indices are designed to help stakeholders plan for bridge maintenance and 

rehabilitation activities. This is typical among weighted averaging and ratio-based approaches,

which calculate the overall health index by combining all defects identified at the element level. 

Other health indices, such as the worst-conditioned component index, are more interested in 

identifying weak links within the bridge structure that could severely affect the safety and 

durability of the bridge in case of a disaster. They are frequently used together with weighted 

averaging methods. Most systems rely on a qualitative approach to assess bridge health and 

performance. Qualitative methods are essential for general assessment of the bridge condition 

and identifying bridges that need maintenance.

With the exception of the recently supplanted SR, all other BMSs rely on element-level 

inspection data to obtain the overall BHI. The use of element-level inspection data provides a 

more thorough assessment of the condition of the bridge. It also provides a more objective 

evaluation of the bridge’s condition because it reduces reliance on inspector’s judgment for 

rating the condition of the bridge. Element-level inspection enables inspectors to capture both the 

severity and extent of any problems that may influence the integrity of the structure. Such 

information is valuable for planning maintenance, repair, and rehabilitation programs.

A key recurring limitation identified is the lack of accurate and objective data used to compute 

the condition indices. Visual inspection remains the predominant approach for assessing the 

condition of bridge elements. Since this heavily relies on human judgment, the possibility of one 

inspector rating the condition state of an element differently from another inspector is likely. 

Therefore, a true assessment of the condition of bridge elements is difficult and uncertain since 

the data acquired is sensitive to the inspector’s expertise and sound judgment. The use of expert 

opinion and engineering judgment, as reflected in assigning weights and defining the relative 

importance of an instance of damage or an element, plays a key role in the estimation of 

condition indices. Opinions about the criticality of an instance of damage or a bridge element to 

the overall structure is highly variable. Using engineering judgment alone may introduce 

subjectivities into the estimation. Therefore, it is safe to conclude that with the current visual 

inspection approach to acquiring bridge condition data, the possibility of subjective and 

imprecise data entering the estimating process is present. The development of condition indices 

should be driven by more objective and quantitative data, which will help bridge managers make 

data-driven decisions.

Studying the basis for the BHIs used around the world also shows that most indices do not 

consider operational, safety, and lifecycle cost performance metrics and mostly rely on condition 

states of the bridge’s elements or components. It is important that an effective performance-
42

based health index includes metrics at different limit states such as utility, operations, 

serviceability, structural, maintenance, safety, resilience, traffic, financial, and environmental.

It should be noted that subjectivity in BHIs will never diminish because some qualitative 

performance metrics always require some level of engineering judgment or input, such as 

condition ratings assignments to bridge elements. Currently, FHWA is establishing researchoriented protocols for data collection during bridge assessment, inspection, NDE, and 

field testing. These protocols could be leveraged in reducing subjectivity when assigning 

qualitative metrics. 
43

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