U.S. Department of 

Transportation

Federal Railroad 

Administration

Characterization of Railroad Bridge Service 

Interruptions

Office of Research

and Development

Washington, DC 20590

DOT/FRA/ORD-13/05 Final Report

February 2013
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February 2013

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Technical Report

4. TITLE AND SUBTITLE

Characterization of Railroad Bridge Service Interruptions

5. FUNDING NUMBERS

DTFR53-00-C-00012

Task Order 236

6. AUTHOR(S)

Richard Joy, Mary Clara Jones, Duane Otter, and Luis Maal

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Transportation Technology Center, Inc.

55500 DOT Road

Pueblo, CO 81001-0130

8. PERFORMING ORGANIZATION 

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

Federal Railroad Administration

Office of Research and Development

1200 New Jersey Avenue, SE

Washington, DC 20590

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AGENCY REPORT NUMBER

DOT/FRA/ORD-13/05

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Program Manager: Monique Stewart

12a. DISTRIBUTION/AVAILABILITY STATEMENT

This document is available to the public through the FRA Web site at http://www.fra.dot.gov.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The Federal Railroad Administration contracted Transportation Technology Center, Inc., to study bridge problems that cause

accidents or service interruptions and to use this information to evaluate the need to develop bridge monitoring systems. Existing 

monitoring systems and other mitigation techniques were also considered. An analysis examining frequency and severity of the 

events estimates that the annual risk exposure from bridge defects is about $98 million excluding costs of resulting train delays. 

The largest contributors are scour, hydraulic problems, and strikes from marine and highway traffic. Another major contributor is 

damage from derailed trains, fires, failed structural members, and moveable bridge problems. A risk control matrix was developed 

to match potential problems with existing control measures and identify areas in which additional controls may be warranted. 

Results suggest that 1) protection systems are more effective than monitoring; 2) bridge inspection is an effective control for many 

potential losses; and 3) significant opportunity exists for defects to be detected by others working on the railway. This may 

indicate that training for recognition of bridge defects may be a cost-effective way of reducing losses from accidents and service 

interruptions. Additionally, track displacement detectors, tilt monitors, and midspan displacement monitors should be considered 

for investigation.

14. SUBJECT TERMS

bridge problems, risk control matrix, Railroad Bridge Service Interruption Database

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74

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ii

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in)

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in)

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft)

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd)

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

1 square inch (sq in, in2) = 6.5 square centimeters (cm2) 1 square centimeter (cm2) = 0.16 square inch (sq in, in2)

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, yd2)

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2)

1 square mile (sq mi, mi2) = 2.6 square kilometers (km2) 10,000 square meters (m2) = 1 hectare (ha) = 2.5 acres

1 acre = 0.4 hectare (he) = 4,000 square meters (m2)

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE)

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz)

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 pounds 

(lb)

= 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg)

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt)

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt)

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal)

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l)

1 gallon (gal) = 3.8 liters (l)

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3)

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

[(x-32)(5/9)] °F = y °C [(9/5) y + 32] °C = x °F

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

Centimeters 0 1 2 3 4 5 6 7 8 9 10 11 12 13

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSIO

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98
iii

Acknowledgments 

The authors express appreciation to all of those who helped with this investigation. Thanks to 

our technical advisory group for reviewing results and key assumptions and providing ideas, 

guidance and support: Mike Coltman and John Choros of the John A. Volpe National 

Transportation Systems Center; Steve Millsap of Burlington Northern Santa Fe Railway 

Company; John Unsworth of Canadian Pacific Railway; Jim Carter of Norfolk Southern (NS) 

Corporation; Mike Freeman of Union Pacific Railroad; and Gordon Davids of Federal Railroad 

Administration Office of Safety.

Thanks also to Jim Richter and Rene Asuncion of Amtrak and to David Bonas, Tom Heinrich,

and Hugh Hyder of NS for their contributions.
iv

Contents

Executive Summary........................................................................................................................ 1

1 Introduction ................................................................................................................. 3

1.1 Background ................................................................................................................. 3

1.2 Objectives.................................................................................................................... 5

1.3 Overall Approach ........................................................................................................ 5

1.4 Scope ........................................................................................................................... 5

1.5 Limitations................................................................................................................... 6

1.6 Organization of the Report.......................................................................................... 6

2 Approach ..................................................................................................................... 7

2.1 Review Industry Literature.......................................................................................... 7

2.2 Query FRA Database................................................................................................... 7

2.3 Interview FRA and Industry Experts........................................................................... 7

2.4 Establish Railway Bridge Service Interruption Database ........................................... 7

2.5 Characterize Bridge Problems..................................................................................... 7

2.6 Economic Analysis...................................................................................................... 8

3 Literature Review ........................................................................................................ 9

3.1 Selected References..................................................................................................... 9

3.2 Mitigation Techniques................................................................................................. 9

3.3 Other Programs to Characterize Bridge-Related Service Interruptions.................... 14

4 Railway Bridge Service Interruption Database ......................................................... 15

4.1 Input from FRA Safety Database .............................................................................. 17

4.2 Input from Railroad Industry..................................................................................... 19

5 Primary Hazards/Precursor Events............................................................................ 20

6 Characterization of Bridge Problems ........................................................................ 22

6.1 Ranking of Primary Hazards by Frequency .............................................................. 22

6.2 Events Resulting in Train Accidents......................................................................... 24

6.3 Damage from External Means................................................................................... 24

6.4 Annual Risk Exposure............................................................................................... 25

6.5 Annual Risk Exposure............................................................................................... 28

6.6 Risk Control Matrix................................................................................................... 30

7 Economic Analysis.................................................................................................... 37

7.1 Upper Limit of Preventable Annual Risk Exposure.................................................. 37

7.2 CBA of Selected Monitoring Systems ...................................................................... 38

7.3 Assumptions and Estimations ................................................................................... 39

7.4 Summary of Economic Analysis............................................................................... 40

8 Summary.................................................................................................................... 42

9 Recommendations ..................................................................................................... 46
v

10 References ................................................................................................................. 47

Appendix A. Risk Control Matrix ............................................................................................... 51

Appendix B. Preventable Annual Risk Exposure for Selected Systems ..................................... 55

Abbreviations and Acronyms ....................................................................................................... 65
vi

Illustrations

Figure 1. Frequency of FRA Reportable Accidents.................................................................. 18

Figure 2. Frequency of Railroad Reported Events.................................................................... 19

Figure 3. Frequency of Industry Bridge Related Service Interruptions.................................... 22

Figure 4. Frequency of Railroad Bridge Failures...................................................................... 23

Figure 5. Highway Bridge Failures in United States from 1966 to 2005 

(presented by Briaud – Texas Transportation Institute) ............................................ 24

Figure 6. Percentage of Failures due to Bridge Deficiencies and External Means................... 25

Figure 7. Ranking of Primary Hazards by Annual Risk – All Data.......................................... 29

Figure 8. Ranking of Primary Hazards by Annual Risk – 1999-2010 Data ............................. 30

Figure 9. Excerpt from Risk Control Matrix............................................................................. 31

Figure 10. Risk Control Matrix Summary .................................................................................. 36

Figure 11. Potential Preventable Annual Risk Exposure by Technology................................... 38

Figure 12. Maximum Cost per Bridge for Technology to Breakeven ........................................ 40

Figure 13. Maximum per Bridge Cost of Track Displacement Detector 

if Installed on 10 or 25 Percent of Bridges................................................................ 41
vii

Tables

Table 1. RBSID Key Fields..................................................................................................... 16

Table 2. High-Consequence FRA Reportable Accidents from 1980 to 1998 ......................... 18

Table 3. Primary Hazards ........................................................................................................ 20

Table 4. Basis for Assigned Loss Values ................................................................................ 26

Table 5. Description of Severity Categories............................................................................ 27

Table 6. Source of Service Interruption Data by Category...................................................... 27

Table 7. Potential Losses Due to Primary Hazards ................................................................. 33

Table 8. Bridge Protection Systems......................................................................................... 34

Table 9. Scheduled Inspections ............................................................................................... 34

Table 10. Existing Detection Systems....................................................................................... 35

Table 11. Advanced/Prospective Mitigation Techniques.......................................................... 35

Table 12. Top 15 Primary Hazards by Frequency..................................................................... 43

Table 13. Summary of Annual Risk Exposure .......................................................................... 44
1

Executive Summary

The Federal Railroad Administration (FRA) contracted Transportation Technology Center, Inc. 

(TTCI), to study the types of bridge problems that cause accidents or service interruptions and to 

use this information to evaluate the need to develop new bridge monitoring systems. Existing 

monitoring systems and other mitigation techniques were also considered.

Data were gathered from the FRA Safety Database, from available railroad company records, 

and from interviews with industry experts. Analysts then developed a preliminary ranking of 

hazards based on frequency and severity of resulting accidents or service interruptions. 

According to the data, the highest number of accidents and service interruptions resulted from 

bridge strikes from highway vehicles and from problems relating to moveable bridge signals. 

Because these are generally low-consequence events, however, they may not represent the 

problems with the greatest overall effect on the railroad industry.

The analysis, which considers both frequency and severity of bridge-related incidents, estimates 

that the annual risk exposure from bridge problems is approximately $98 million. The largest 

contributor is scour from moving water, combined with other bridge hydraulic problems at about 

$26 million per year. Next in rank are strikes from marine traffic at about $22 million per year 

and strikes from highway vehicles at about $11 million per year. Another large contributor is 

damage caused by derailed trains, fires, failed structural members, and moveable bridge 

problems. 

Over 25 percent of the $98 million is attributable to four significant accidents that occurred 

between 1982 and 1997. No risk exposure events of this magnitude have occurred since 1997. 

This simplified approach does not consider improved procedures put in place by railroads and 

other entities since the events have occurred. 

A risk control matrix was developed to match potential problems with existing control measures 

and to identify those areas where additional controls may be warranted. Results suggest that:

• Protection systems are likely more effective than monitoring.

• Bridge inspection is an effective control for many potential losses. It is currently the first 

line of defense for the railroads.

• Significant opportunity exists for defects to be discovered by others working on the 

railway. This may indicate that training for recognition of bridge defects may be a costeffective way of reducing losses from bridge accidents and service interruptions.

• Track displacement detectors, tilt monitors, and midspan displacement monitors should 

be considered for additional investigation.

The estimates of risk exposure were used for a preliminary economic analysis of 15 potential 

monitoring systems. Of the 15 systems considered, 7 had annual upper limits of preventable 

annual risk exposure between approximately $13 and $36 million. The remaining eight systems 

had annual upper limits of approximately $5 million or less. 

To provide a comparison of potential systems, a basic cost-benefit analysis (CBA) was 

conducted on six of the seven selected potential monitoring systems. The analysis considered
2

the maximum initial cost per bridge that could be spent on a system based on the preventable 

annual risk exposure. Results indicate that for implementation of any of the systems to be costeffective, a selective implementation strategy would be required. Across-the-board 

implementation would not be cost-effective. 

The estimates of costs reported here were used to rank the primary hazards. Costs of train 

delays, traffic diversions, and business loss are not included. These analyses are intended for 

initial comparisons only.

A literature review was carried out to identify existing and potential monitoring systems and to 

identify similar work that has been undertaken. An industry technical advisory group (TAG) 

was formed consisting of high-level railroad bridge engineers, the John A. Volpe National 

Transportation Systems Center (Volpe), and FRA.

Data were gathered from the FRA Safety Database, from available railroad company records, 

and from interviews with industry experts. Both FRA and railroad data lack detail. However, 

the available data were unified and collated in a Railroad Bridge Service Interruption Database 

(RBSID), which contains over 8,700 records. The database was created in Microsoft Access to 

allow for easy entry and query.

Additional work is proposed to develop a risk assessment method that would identify those 

bridges that will benefit most from having remote monitors installed and to identify technologies 

that can aid the inspection process. This might include improved nondestructive evaluation 

(NDE) techniques or bridge health monitoring technologies.
3

1. Introduction

The objective of this project was to gain a better understanding of the types of bridge problems 

that cause accidents or service interruptions and to use this information to evaluate the need to 

develop new bridge monitoring systems. Existing monitoring systems and other mitigation 

techniques were also considered. 

1.1 Background

Recent events such as the I-35 highway bridge failure in Minneapolis, MN, and the railroad 

bridge accident in Myrtlewood, AL, have renewed interest in remote monitoring as a means of 

protecting critical infrastructure. In the United States, railroad bridges are a critical part of the 

transportation network. According to a recent FRA study there are over 1,760 miles of railroad 

bridges in the United States, including 418 miles of timber structures (1).Thousands of steel 

bridge spans approaching 100 years of age are still in service.

Commercial bridge monitoring systems are becoming more common. A recent survey 

documents 38 companies that supply bridge monitoring equipment (2). However, the survey 

authors caution that, although many of the systems come with claims that results would be 

immediately useful to the owner, much study is still needed to establish useful thresholds. The 

best information that most systems can offer today is a warning that changes have taken place.

1.1.1 New Regulations for Railway Bridges

In response to a series of train accidents caused by failures of timber bridges, FRA issued a 

safety advisory in September 2007 to supplement and re-emphasize the provisions of the Policy 

on the Safety of Railroad Bridges(3).

On October 16, 2008, the Rail Safety Improvement Act of 2008 was signed into law. The new 

regulations required railroad track owners to adopt and follow specific procedures to protect the 

safety of their bridges. In response, on August 17, 2009, new U.S. bridge safety regulations were

formally proposed by FRA. These regulations were developed in cooperation with industry 

through a Rail Safety Advisory Committee. The Final Rule was published on July 15, 2010, as 

Title 49, Code of Federal Regulations, Part 237 (4).

1.1.2 Selected Significant Bridge Events

A number of key events on both highway and railroad bridges have driven bridge policy in the 

United States.

I-35 Bridge Failure – Minneapolis, MN

On August 1, 2007, a highway bridge carrying Interstate 35 over the Mississippi River in 

Minneapolis, MN, collapsed during rush hour traffic causing 13 fatalities. Since the accident, 

increased public awareness has created a renewed interest in critical infrastructure condition, 

management, and monitoring in the United States (5).
4

Railway Bridge Accident in Myrtlewood, AL

On May 2, 2007, a freight train carrying segments of the space shuttle’s solid rocket boosters 

derailed in Myrtlewood, AL, after a timber trestle collapsed. The train comprised cars of 

exceptional weight and configuration and was operating without proper clearance from the track 

owner. This incident has been cited as a reason behind a new set of FRA regulations proposed in 

August 2009 (3).

Amtrak Derailment in Kingman, AZ

On August 9, 1997, in Kingman, AZ, an Amtrak train derailed as it was crossing a bridge. It was 

later determined that the bridge’s supporting structure had been washed away by a flash flood

(6).

Derailment on Portal Bridge in Secaucus, NJ

On November 23, 1996, Amtrak train No. 12 derailed while crossing Portal Bridge, a swing 

bridge spanning the Hackensack River in Secaucus, NJ. When the train derailed, it sideswiped 

Amtrak train No. 79, which was crossing the bridge in the opposite direction on an adjacent 

track. Cause for derailment was found to be defective rail-end transition devices (7).

Amtrak Accident on Big Bayou Canot Bridge near Mobile, AL

On September 22, 1993, an Amtrak train derailed because one span of the Big Bayou Canot 

Bridge near Mobile, AL, was out of alignment after being struck by a barge. The train arrived 

and derailed at the bridge less than 10 minutes after the incident. There were 103 injuries and 47 

fatalities (8).

Failure of the Schoharie Creek Highway Bridge near Amsterdam, NY

On April 5, 1987, the Schoharie Creek Highway Bridge near Amsterdam, NY, failed because of

scour damage at pier three of the bridge. Ten people were killed. It was later determined that 

the installation of riprap, used to protect from scour, had been cancelled. This accident 

motivated the improvement of bridge inspection, maintenance, and management practices (9).

Collapse of Route 95 Highway Bridge in Greenwich, CT

On June 28, 1983, the Route 95 Highway Bridge over the Mianus River in Greenwich, CT,

collapsed, killing three people, because the pin and hanger assembly supporting the span failed

(10).

Collapse of Silver Bridge between West Virginia and Ohio 

On December 15, 1967, the Silver Bridge between Point Pleasant, WV, and Kanauga, OH,

collapsed, killing 46, because of an eyebar failure. This accident led to legislation requiring a 

national bridge inventory, biennial inspections, inspector qualifications, and reporting

requirements (11).
5

1.2 Objectives

The long-term objective of this project is to identify bridge monitoring systems that will warn

bridge owners of possible structural damage, reduce the occurrence of bridge problems by 

providing early warning of bridge distress, and enable predictive maintenance on an aging bridge 

population. 

1.3 Overall Approach

This work focused on developing detailed characterizations of the major drivers causing 

accidents or service interruptions. The first source of information was the FRA Safety Database,

which records accidents involving train operations. In addition, available data from five major 

railroads were compiled. Also, the FRA Office of Safety was consulted to review and augment 

the available data. To encourage participation and cooperation, railroad names are not 

reported—industrywide summary information is used.

Simple risk analysis techniques and economic analyses were used to estimate what problems 

have the greatest effect on the industry and how bridge monitoring or other techniques may best 

be used to mitigate the problems. Existing railroad bridge monitoring systems, potential 

advanced monitoring systems, and other mitigation techniques were considered.

An industry TAG was established to guide the work.

1.4 Scope 

The FRA Safety Database identifies bridge failures, but the cause codes do not focus narrowly 

enough to understand what is required to reduce risk in a particular area. Furthermore, only 

events above a damage cost threshold and involving train operation are included. 

The RBSID compiled for this investigation includes data from the FRA Safety Database and 

from the railroads. Unlike the FRA data, railroad information includes major events that did not 

involve train operations such as bridge fires and bridge washouts. In addition, many less serious 

but frequent events are included. For example, bridge strikes by highway vehicles often result in 

little or no damage, but interrupt railroad traffic while inspections are carried out. The RBSID 

will be provided to FRA as part of the deliverables for this project.

The information compiled in the RBSID was used as the basis for a simplified risk analysis to 

show what types of events and hazards are having the greatest affect on the industry. A list of 

primary hazards driving the identified bridge problems was compiled. Existing and potential 

bridge monitoring systems and other mitigation techniques were matched to the primary hazards 

with the greatest effects.

The information compiled for the risk analysis was used for a preliminary economic analysis to 

estimate how much could reasonably be spent on implementation of selected monitoring systems 

and technologies. Results indicate that cost-effective implementation of any of the systems will 

require a selective implementation strategy. Across-the-board implementation would not be 

cost-effective. Additional work is recommended to design a structured, risk-based approach for 

selective implementation of monitoring systems.
6

1.5 Limitations

The simplified risk analysis in this report provides a reasonable insight into what has driven 

bridge-related accidents in recent years. Events compiled over the past 10 years provide a good 

picture of high-to-medium frequency, low-to-medium consequence events driving accidents and 

service interruptions. 

High-consequence events such as the Big Bayou Canot or Kingman, AZ, accidents have been 

infrequent, particularly in recent years. This is largely due to railroad’s incorporation of best 

practices in bridge inspection and management. Over the past 30 years, there have been only 

four of these high-consequence accidents. Once the annual risk was compiled, the cost was 

normalized over a 30-year period. This simplified approach does not consider improved 

procedures put in place by railroads and other entities since the events occurred.

A comprehensive analysis of potential high-consequence events would need to consider not only 

historical events but potential future events. Although methods exist for such an analysis, it is 

beyond the scope of this report. Any additional work for selective implementation of monitoring 

systems will need to use a structured approach to consider the possibility of events that have not 

been documented historically.

The risk analysis incorporated rough estimates of loss based on the bridge service interruption 

data compiled. Because of the large number of bridge events considered, a number of very 

general estimates were used. Where actual values of loss were available, a multiplier was used 

to account for indirect damage. It is recognized that indirect costs can vary widely. Total values 

are somewhat understated because the multiplier does not account for train delay, traffic 

diversion, and business loss costs. In the majority of cases in which actual values of loss were 

not available, a structured approach for applying order-of-magnitude estimates was applied. 

The estimates of costs reported here were used to rank the primary hazards. These analyses are 

intended for initial comparisons only.

1.6 Organization of the Report

This report is organized into six main areas:

• Results from Industry Literature Review

• Railway Bridge Service Interruption Database

• Characterization of Bridge Problems

• Economic Analysis

• Summary

• Recommendations
7

2. Approach

To identify the types of bridge failures that cause accidents or service interruptions and to 

determine when and what type of monitoring is warranted, TTCI studied and characterized 

bridge risk factors and how these risk factors might be mitigated.

2.1 Review Industry Literature

A literature search was conducted to document existing and potential bridge protection,

monitoring techniques, and other efforts that characterize causes of railway or highway bridge 

service interruptions.

2.2 Query FRA Database

The FRA Safety Database of rail-related accidents and other incidents was queried for bridgerelated events. The available information is limited because the database generally contains only 

relatively serious accidents involving train operation. 

2.3 Interview FRA and Industry Experts

An industry TAG was formed to provide feedback and direction in the project. The participating 

groups included Amtrak, Norfolk Southern Corp. (NS), Union Pacific Railroad (UP), Burlington 

Northern Santa Fe Railway Company (BNSF), Canadian Pacific Railway (CP), FRA Office of 

Research, FRA Office of Safety, and the John A. Volpe National Transportation Systems Center 

(Volpe). Periodically, the TAG was asked to comment on results and to review key assumptions 

used in the study.

In addition, followup interviews were carried out where required. The authors visited BNSF, 

NS, and Amtrak offices and held phone conversations with the FRA Office of Safety.

2.4 Establish Railway Bridge Service Interruption Database

Data from various sources were unified and collated into a useful form in the RBSID. 

Derailments from the FRA Safety Database and service interruptions provided by five major 

North American railroads are included. The RBSID contains over 8,700 records. It was created 

in Microsoft Access to allow for easy entry and query.

2.5 Characterize Bridge Problems

The RBSID was analyzed in detail to develop a characterization of the types of bridge problems

that are causing accidents and service interruptions. A simplified risk analysis approach was 

used to identify the primary hazards most likely to result in accidents or service interruptions and

to identify potential control or mitigation measures for these hazards. 
8

2.6 Economic Analysis

A preliminary economic analysis was carried out for 15 selected potential monitoring systems

likely to be the most effective. Information from the RBSID was used to establish an upper limit 

of the preventable annual risk exposure that each monitoring system might address. Then, 

discounted cash flow techniques were used to estimate how much spending could be justified for 

six of the most promising monitoring systems.
9

3. Literature Review

A literature review was conducted to review current and developing mitigation techniques. In 

addition, similar efforts to categorize bridge problems were reviewed. For convenience,

information provided by the industry TAG is included in the report.

3.1 Selected References

The following references are excellent summaries of bridge monitoring needs and technologies 

and are most relevant to this investigation.

In 2009, the University of Minnesota prepared a report on bridge health monitoring methods for 

the Minnesota Department of Transportation (MNDOT) (2). The report is intended for highway 

bridge engineers. It is an excellent and current reference for railway bridge engineers as well. 

The report lists survey results from 38 companies that supply bridge monitoring equipment. The 

authors draw an important conclusion that although many companies offer complete monitoring 

systems that would be immediately useful to the owner, much work still needs to be done to 

establish useful thresholds. The best information that most systems can offer today is a warning 

that changes have taken place, which suggests that damage likely exists.

In 2008, the Transportation Research Board (TRB) published an article by Hunt on scour 

monitoring programs for bridge health (12). It reports on scour monitoring of four bridges that 

incorporated site-specific fixed scour monitoring. The scour monitoring included a fixed sonar 

system for tidal-cold weather environment, a multiple station sonar system, and a scour 

monitoring program manual. The scour monitoring program reviewed available data (historic, 

current, and potential) to evaluate scour conditions, performed a hydraulic, scour, and stability 

analysis of the bridge, and evaluated scour countermeasure alternatives. Most notable for this 

evaluation was a general discussion highlighting lessons learned from past scour monitoring and 

trends in scour monitoring technology.

The International Heavy Haul Association included an article on Bridge Health Monitoring in its 

Guidelines to Best Practices for Heavy Haul Railway Operations (13). It provides an excellent 

overview of railroad bridge monitoring systems currently being used in North America and is 

cited several times in this report.

In 1994, FRA conducted a study on railroad bridges to assess techniques and technologies for 

automatic monitoring of railroad bridge integrity for the purpose of reducing the number of 

bridge-related train accidents (14). Results indicated that widespread installation of bridge 

monitoring devices was not economically feasible. However, the study did not rule out bridge 

integrity monitoring on bridges highly vulnerable to damage. 

3.2 Mitigation Techniques

For the purpose of this investigation, mitigation techniques were categorized as bridge protection 

methods, scheduled inspections, existing monitoring systems, and advanced or prospective 

mitigation techniques. 

Davids of the FRA Office of Safety emphasizes that good bridge inspections are the first and last 

line of defense against bridge failures, catastrophic and otherwise (15). Davids points out that 
10

bridges do not often just fail without warning indications, and the purpose of a bridge inspection 

is to find those indications before they turn into serious problems. Inspections should be 

scheduled at a sufficient frequency and a level of detail that these indications can be found in 

time. Highway bridges are required to be inspected once every 2 years. Davids notes that an 

industry standard of annual inspections for railroad bridges dates back more than 100 years. This 

standard has recently been incorporated into the Final Rule on Railroad Bridge Safety (4).

Bridge protection methods generally provide high value because they can prevent damage from 

occurring rather than just reporting that is has occurred. Similarly, some bridge monitoring 

techniques can provide advance warning to identify potential problems and warn the train 

operator that a hazard exists. Traffic can be stopped through a radio alarm, signal system, or 

notification sent to the dispatcher.

Other monitoring systems provide an indication of a bridge’s overall health. Otter and Carr

suggest that these systems provide a great deal of data and require interpretation of results by a 

bridge engineer (13).

3.2.1 Bridge Protection Methods

Bridge protection methods generally refer to physical barriers to bridge damage. Techniques for 

protection against bridge strikes include protecting the piers with crash walls, barrels, beam 

guardrail, cable, and/or concrete (16). Waterway bridge protection methods are used to protect 

bridges that cross or are near navigable waterways. Appropriate lighting is required per U.S. 

Coast Guard regulations. Bridges near or at these waterways typically use fenders to protect 

bridge piers from barge and ice or drift strikes (13). 

Several other bridge protection methods are available. Sacrificial beams are used in some cases 

to protect bridges from overheight vehicles. Signage, lighting, painting, pavement markings, and 

telltales have also been used on roadways approaching low-clearance overhead railroad bridges. 

The industry TAG identified inner guardrails, truss guardrails, and truss collision posts as 

common means of preventing or minimizing bridge damage from derailed trains.

3.2.2 Scheduled Inspections

The American Railway Engineering and Maintenance and Way Association (AREMA) has 

recently published a comprehensive bridge inspection handbook (17). The handbook covers all 

facets of railway bridge inspections, such as special inspections after fires, floods, derailments,

or earthquakes. A recent paper by Sweeney and Unsworth provides details of inspection 

programs for two large North American railroads (18).

For highway bridges, the National Cooperative Highway Research Program has published a 

report on bridge inspection practices in the United States and selected foreign countries (19). It 

is a collection of information on formal inspection practices of departments of transportation. 

Information is presented on inspection personnel, inspection types, and inspection quality control 

and quality assurance. 

The industry TAG indicates that some railroads are training track inspectors to carry out basic 

bridge inspections as part of their regular duties as a way to supplement their bridge inspection 

programs.
11

Detailed inspections of moveable bridges usually require a team of inspectors with one each 

from mechanical, electrical, and structural disciplines (17). The industry TAG notes that many 

of the moveable bridge problems are reported by either local or remote bridge tenders or 

operators. In addition, moveable bridge problems are often detected as a signal system 

interlocking failure.

NDE methods such as dye penetrant and ultrasonic inspection are often used to supplement 

scheduled inspections of railroad bridges. A new program developed by the Federal Highway 

Administration (FHWA) presents a 1-day seminar to provide formal training to bridge inspectors 

in the basic principles and general operational procedures of five of the latest portable, 

technician-driven NDE technologies: (1) ultrasonic testing, (2) eddy current, (3) ground 

penetrating radar, (4) impact echo, and (5) infrared thermography (20). These technologies are 

intended to supplement scheduled bridge inspections on an ongoing basis.

Underwater inspections are critical on many bridges. The AREMA Bridge Inspection Handbook

notes that the need for and frequency of underwater inspections is determined by an engineer for 

any structure having continuously submerged components (17).

3.2.3 Existing Detection Systems

A number of existing detection systems are either currently being used on bridges or can be 

adapted for such use. Otter and Carr identify shifted load and high or wide load detection and 

dragging equipment detection as technologies that are commonly being used in North America

(13). 

High-water detectors are advance warning systems where train crews, maintainers, and other 

personnel can be alerted to high water at a particular bridge. High-water detectors are potentially 

useful in identifying conditions likely for scour to occur. These systems can be connected 

through a radio alarm, signal system, or notification sent to the dispatcher to stop traffic if 

necessary, often based on a threshold monitoring value (13).

Shifted load and high or wide load detection systems are used to prevent bridge strikes where a 

rail vehicle does not have enough clearance for the bridge or tunnel. These systems check 

vehicles or loads that are too large to safely clear the bridge or tunnel. Again, radio or other 

notification can be used to stop the train (13). 

Dragging equipment detectors identify railcars that could cause significant damage to a bridge. 

These detectors are very useful in identifying derailed wheels (13). 

The industry TAG points out that the rail-break circuit of the signal system can also be 

considered a bridge monitoring device, because identification of a rail break on or near a bridge 

can prevent potential damage from a train derailment. 

Load monitoring is an important tool used to monitor bridges. For many bridges, the load rating 

for the bridge when installed is inadequate today or will be inadequate with increased axle loads

or increased traffic. Chase and Laman discuss several technologies that have been used to 

monitor loads in bridges including piezoelectric sensors (ceramic and polymetric), optical 

sensors (microbend and Bragg grating), and interferometric (21). Otter and Jones describe an 

Association of American Railroads’ (AAR) program to measure the load traffic on railroad 

bridges (22). A wayside detector that measures vertical load (wheel impact load detector) is used 
12

to estimate the vertical load railroad cars are putting on bridges. Witte et al. describe how wheel 

impact load detectors can be used to detect imbalanced loads, which can reduce bridge life over 

time (23).

Damage to bridges due to train accidents caused by track buckling on approaches is a significant 

problem. Track buckling occurs in continuous welded rail when high compressive forces build 

up. Rail strain monitoring technologies can identify track conditions where high compressive 

loads exist. Read describes a number of technologies that exist to monitor rail strain (24). 

Electrical resistance strain gages are simple to install but require cutting of the rail to obtain a 

calibration when the rail is unloaded. These systems are capable of continuous monitoring but 

are location specific and cannot be moved to a different location. Some are equipped with radio 

freqency technology to allow remote monitoring.

Picton Technologies has developed a simple technology that can provide warning of an 

unacceptable track displacement (25). It is based on a simple contact switch that is broken after 

a predetermined deflection. The switch can be integrated with the current signal system.

Reece et al. describe how geographic information system (GIS)based weather notification 

networks that can provide automated warnings of severe weather to railroad dispatch centers are 

being used by major North American railroads (26). The GIS notifications are location specific, 

which allow the railroad to take early action such as delaying trains or dispatching inspectors to 

avoid accidents. Notifications of heavy storms that may result in flash floods are particularly 

applicable to bridges.

Railroads in North America rely on earthquake notifications systems to provide automatic 

notification of significant earthquakes (27) Guidelines for post earthquake operation are 

provided in the AREMA Manual for Railway Engineering, Chapter 9 (28).

The industry TAG points out that many bridge problems are found by those other than bridge 

inspectors, i.e., track inspectors, bridge tenders, locomotive engineers, signalmen, or others,

while carrying out their normal duties. One Class 1 railroad has prepared a training course for 

track inspectors on how to detect potential water-caused problems. This has proved very 

effective with regard to high water, blocked water courses, etc.

3.2.4 Advanced or Prospective Mitigation Techniques

A number of advanced or prospective mitigation techniques were considered based on the 

literature and discussions with the industry TAG. The set of techniques considered for further 

evaluation is not exhaustive but covers many concepts being considered by the industry.

Strainstall offers a detector to identify when a bridge strike occurs; however, these are not widely 

used in the United States (13, 29). 

Deflection of a bridge span under loads is often considered an important parameter for bridge 

performance evaluation. However, it is often inconvenient to obtain the bridge deflections 

directly. Difficult access when bridges cross rivers, other railways, or highways makes a direct 

measurement impractical. Gindy et al. report on an experiment to use integrated acceleration to 

measure deflection in these difficult areas (30). To date, sensor drift, unknown initial bridge 

conditions, and dynamic coupling with the traffic loads have proved these measurements to be 
13

unreliable. However, MNDOT reports that several companies claim to offer displacement 

measurements and data interpretation (2). 

Hunt describes several methods for unattended scour monitoring (12).

• Sonar scour monitors, which are mounted onto the pier or abutment face and connected 

to data loggers. These monitors track the scour and refill process.

• Magnetic sliding collars are rods attached to the pier or abutment face with sliding 

magnetic collars that rest on the streambed. Should the streambed erode, the collars 

move downward. These devices measure the maximum depth of scour rather than the 

scour and refill process.

• Float-out devices are buried at various depths near the substructure. If scour develops, 

the devices float to the surface and transmit a signal.

• Tiltmeters and vibration meters to monitor bridge movement.

A scour monitoring system may be a single device or a combination of the above devices. Data 

may be downloaded at the site or transmitted to a central location.

Strain measurement techniques are often used on steel bridges to quantify actual stresses in 

problem areas identified during bridge rating. Najjar et al. and Kober et al. provide excellent 

case studies (31, 32). Often the mesured stresses are significantly less than those calculated 

because of unexpected member load sharing, etc. MNDOT reports that a several companies are 

now offering systems that use strain measurement as part of a global health monitoring system

(2).

Hunt reports that tilt monitors can be used as part of a scour monitoring system to detect gradual 

movements of foundations (12). MNDOT suggests that because inclination must be known at

more than one point on a bridge to provide usable information, a single tilt monitor would not be 

a viable bridge monitoring method (2), although several vendors offer tilt monitoring as part of a

bridge monitoring system.

Monitoring systems mounted on bridges have a built-in limitation in that they can only monitor 

the bridge they are installed on. The industry is interested in developing a vehicle-borne system 

that can detect bridge problems as it travels over the system. AAR is investigating the feasibility 

of such a system under its Strategic Research Initiatives. Arnold et al. have developed a system 

that measures track modulus from a moving rail car (33). Analysis of these data has been able to 

identify weak track at bridge approaches. There may be potential to adapt such a system to 

identify unacceptable deflection of bridges.
14

3.3 Other Programs to Characterize Bridge-Related Service Interruptions

FHWA has initiated a Long-Term Bridge Performance (LTBP) Program to collect nationwide 

data on highway bridges (34). This will be a 20-year research effort. Data will be collected from 

different sources including legacy data, detailed visual inspection reports, environmental 

information, and monitoring or instrumentation data. To efficiently manage, organize, and use 

this vast amount of data, LTBP is developing an open, scalable, and extensive data management 

and analysis infrastructure.

Stein and Sedmera report on a 2006 study of risk-based management guidelines for scour. The 

work was sponsored by the American Association of State Highway and Transportation Officials 

in cooperation with the FHWA (35). This program developed guidelines to select a management 

plan for preventing scour failure for bridges with unknown foundations. The guidelines included 

collecting appropriate data, estimating risk of failure, and selecting a bridge management 

approach.

The Rail Safety and Standards Board in the United Kingdom published a report analyzing the 

rising trend in the number of reported bridge strikes from 1994 to 2001, with the aim of 

understanding the reasons for this trend (36). On average, 30 bridge strikes occur each week over the 

British railway system, approximately 96 percent of which result in little or no consequential 

damage.

In its report on bridge monitoring methods, MNDOT included a systematic methodology for 

matching bridge monitoring needs with available technologies, using a Microsoft Excel spreadsheet 

program.2
15

4. Railway Bridge Service Interruption Database 

The RBSID contains information on over 8,700 accidents and service interruptions based on 

FRA and industry records. Industry records were included specifically to capture service 

interruptions not included in the FRA database and to clarify some ambiguous entries. The 

information is in a Microsoft Access database. 

A record is filed for each event that resulted in an accident or service interruption. Each record 

contains 29 data fields that have been completed based on the availability of data. Table 1 lists

the fields with a brief description of each.
16

Table 1. RBSID Fields

Field Description

Incident Number Unique reference number

Service Interruption (Yes/No) Did the event cause a service interruption?

Length of Service Interruption (hour) If known

Primary Hazard Primary hazard as described in Section 5

Type of Damage

If known — bridge collapse/partial collapse, 

misalignment, damage to substructure, damage to 

superstructure, etc.

Severity Category 1, 2, 3, or 4

Cause 1 Allows for additional explanation of cause

Cause 2 Allows for additional explanation of cause

Cause 3 Allows for additional explanation of cause

Year Year event took place

Source of Incident Data Source of data -- Railroad, FRA, or other

Source of Report If known — how was event reported -- dispatcher, 

citizen call-in, bridge inspector, etc.

Equipment Damage ($) If known — cost of equipment damage

Track Damage ($) If known — cost of track damage

Total Property Damage ($) If known — total cost of property damage

Number of Injuries Self-explanatory

Number of Fatalities Self-explanatory

Super Structure Material If known — steel, timber, etc.

Super Structure Type If known — girder, truss, beam, etc.

Substructure Type If known — deep foundation, shallow foundation, 

other

Moveable Yes or no

If Moveable, what type? Bascule, vertical lift, etc.

Deck Type Open deck, ballast deck, other

Feature Crossed Other railroad, highway, navigable waterway, etc.

Height Clearance (ft) If known

Short Description of Incident As available — modified as necessary to avoid 

revealing railroad names

Comments Allows authors to add comments
17

4.1 Input from FRA Safety Database

FRA maintains a Safety Database on rail-related accident and incident occurrences. Anyone 

may download this data from the FRA Web site (37). All accidents or incidents that involve rail 

equipment in the United States and result in equipment and track damage greater than a dollar 

threshold set annually by FRA must be reported and included in the database. With a few 

exceptions, bridge problems that do not involve a train, such as a washout or a fire, are not 

included. Threshold dollar values range from $6,700 in 1999 to $9,200 in 2010. Reporting 

requirements are described in the proposed “FRA Guide for Preparing Accident/Incident Reports

(38).”

The most important FRA Safety Database entries for this investigation include accident causes, 

estimated dollar amount of equipment and track damage, total property damage, and the number 

of fatalities and injuries. A short narrative description is also provided, which was essential to

extracting bridge-related events. 

There are 389 cause codes used in the FRA Safety Database ranging from mechanical failure 

codes to human error codes. Some examples are: cause code E30C — Knuckle Broken or 

Defective, cause code M201 — Load Shifted, and cause code T201 —Broken Rail – Bolt Hole 

Crack or Break. The only cause code specifically used for bridges is T401 — Bridge 

Misalignment or Failure. Cause code T499 — Other Way and Structure Defect with Detailed 

Description is sometimes used for bridge problems. However, many accidents involving bridges 

are listed under other codes.

All accidents for the appropriate period were downloaded from the database. The data were 

queried for the two bridge-related cause codes. However, many additional accidents involving 

bridges were found by searching the narratives for the key word “bridge.” Many of these 

accidents were due to external means. One example would be a train derailment caused by a 

burned off bearing where a bridge was struck and damaged. This accident would be listed with a 

mechanical failure code. It could only be identified as a bridge-related event by searching the 

narrative by key word. Some accidents involving bridges had no reference to a bridge but were 

found by correlating FRA data with railroad-supplied data.

All bridge-related accidents from the period from January 1999 to March 2010 are included in 

the RBSID. No high-consequence events such as the Big Bayou Canot or Kingman, AZ,

accidents occurred during this period. 

An additional query for accidents with an estimated total cost over $20 million over the period 

between January 1980 and December 1998 revealed four of these high-consequence accidents. 

Table 2 shows these accidents. These accidents have also been included in the RBSID.

The Myrtlewood, AL, accident is included in the 1999–2010 data, but the total cost is 

significantly less than $20 million.
18

Table 2. High-Consequence FRA Reportable Accidents from 1980 to 1998

Year Description

Estimated Cost 

(millions —

2010 dollars)

Injuries/

Fatalities

1982 Derailed six cars due to bridge washout and 

excessive speed for conditions.

$20.9 15/0

1993

Train derailed because one span of the Big Bayou 

Canot bridge near Mobile, AL was out of 

alignment after being struck by a barge

$436.2 103/47

1996 Train with two engines and 12 cars derailed the 

entire consist at Portal Bridge, Secaucus, NJ. As 

train was derailing, it sideswiped westbound train

$64.1 43/0

1997 Derailed 15 cars on bridge in Kingman, AZ,

which had been damaged by runoff because of

heavy rain

$242.1 183/0

Figure 1 shows the number of bridge-related accidents from 1982 to March 2010 by the related 

primary hazard. There were a total of 177 accidents. The highest number of accidents (22 

percent) was caused by derailed trains, followed by load shift (9 percent).

22.6%

9.6%

7.9%

6.8%

5.6% 5.1% 5.1% 5.1% 4.5%

2.8%

4.5%

3.4% 3.4% 2.8%

1.7%

9.0%

0%

5%

10%

15%

20%

25%

Figure 1. Frequency of FRA Reportable Accidents
19

4.2 Input from Railroad Industry

Bridge service interruption data were provided by five major railroads, and it greatly expanded 

the data from the FRA Safety Database. Unlike the FRA data, many events not directly caused 

by the movement of trains such as fires and bridge washouts were included. In addition, data 

from the railroads included many lower-consequence events with damage less than the threshold 

for FRA reporting.

As part of the data-gathering process, the TTCI team visited three Class 1 railroad offices and 

interviewed senior bridge engineers. The industry data collected varied widely from railroad to 

railroad. Some railroads provided detailed description of each service delay including the delay 

time, whereas others provided input based on the recollection of key personnel. Where data 

were based on recollection, an estimate of annual service interruptions was compiled, with 

estimates of severity and the underlying cause. These estimates were extrapolated over 10 years 

and included in the RBSID.

There is little railroad data available that is older than 10 years, and the available data generally 

lack detail. Costs are not available in most cases.

Figure 2 provides a summary of industry bridge-related service interruptions. There are a total of 

8,563 events reported. The highest frequency event is strikes by highway vehicles representing 

approximately 50 percent of the data.

49.9%

35.3%

5.2% 2.1% 1.8% 1.5% 1.0% 0.9% 0.8% 0.4% 0.2% 0.2% 0.2% 0.1% 0.1% 0.4%

0%

10%

20%

30%

40%

50%

60%

Figure 2. Frequency of Railroad Reported Events 
20

5. Primary Hazards/Precursor Events

The study conducted by FRA in 1994 listed 15 initiating causes of bridge accidents. Because 

service interruptions as well as accidents are included, the list was expanded as the events in the 

RBSID were analyzed. A number of additional hazards were included based on suggestions 

from the industry TAG. 

For the purpose of this investigation, these precursor events or conditions are referred to as 

primary hazards. The authors have attempted to group similar hazards where appropriate, while 

leaving those hazards with unique features separate. Table 3 lists the 43 primary hazards 

identified.

Table 3. Primary Hazards

Primary Hazard

Bridge Approach Problems Load Shift

Bridge Misalignment Bridge Strike—Marine Traffic

Broken Rail on Bridge Moveable Bridge Mechanism

Corrosion (steel structures) Moveable Bridge Signals

Decay/Rot (timber structures) Mudslide/Landslide

Defect Found during Inspection Other Hydraulic—Bridge

Damage by Derailed Train Other Track Defect

Deterioration—Concrete Overload

Earthquake/Tsunami Rail Car Defect

Failed Structural Member Bridge Strike—Railroad Traffic

Falling Debris Sabotage/Explosion

Fatigue(steel structures) Scour

Fire Storm/Hurricane

Foundation Problems Structural Damage Because of

Vandalism

Hanging Wires Track Buckle/Kink

High/Wide Rail Carload on Bridge Track Geometry

Bridge Strike—Highway Traffic Track Washout

Hydraulic—Approach Unknown

Imbalanced Load Unsafe Walkway

Improper Design/Construction Wide Gage

Improper Operation of Maintenance of 

Way Equipment

Wind
21

Problems related to high water are separated into three primary hazards: (1) Scour, (2) Other 

Hydraulic—Bridge, and (3) Hydraulic—Approach. Scour implies an undermining of the 

foundation because of high flows. Other Hydraulic—Bridge includes bridge washouts, ice, or 

debris buildup or poorly described high-water problems. Hydraulic—Approach refers to a 

washout or other high-water damage to the bridge approach.

There are many events in the RBSID having multiple causes or lacking details that would point 

to a cause. An attempt was made to associate every event with a primary hazard. FRA Office of 

Safety was consulted and, in many cases, provided sufficient clarification to identify a primary 

hazard. However, in six cases engineering judgment was insufficient, and the primary hazard 

was listed as unknown.

Also, there are several cases in which one could arguably combine several primary hazards under 

a single heading or split a hazard into several subheadings. For example, Track Buckle/Kink,

Track Geometry, Track Washout, and Wide Gage could be combined under the heading of 

Derailed Train. However, in this case, the authors decided to keep them separate. Damage from 

a derailed train is likely to be the result of a mechanical problem or another problem that occurs 

far from the bridge. Sun kinks, wide gage, and other track geometry issues are problems 

occurring at the bridge or approach.
22

6. Characterization of Bridge Problems

The RBSID was analyzed in detail to develop a characterization of the types of bridge problems

that are causing service interruptions. The analysis was meant to reduce the list of primary 

hazards from a list of 43 to a more manageable number. Similarly, the analysis identifies several 

mitigation techniques for further evaluation.

Each of the RBSID events was associated with one of the primary hazards. To consider both 

frequency and severity of resulting accidents or service interruptions, a simplified risk analysis 

approach was used. This analysis identified the primary hazards most likely to result in the 

greatest loss to the industry. Potential effects of various mitigation measures for the hazards 

resulting in the greatest estimated loss were explored. CBAs were carried out for those 

mitigations likely to have the greatest effect.

6.1 Ranking of Primary Hazards by Frequency

Figure 3 shows a breakdown of all bridge-related service interruptions or accidents in the RBSID 

by the related primary hazard. There are a total of 8,740 events. The largest number of events 

(49 percent) is due to bridge strikes from highway traffic. Service interruptions related to 

moveable bridge signals comprise 35 percent of the database. The remaining 16 percent of the 

events are related to other causes. Although events related to bridge strikes and moveable bridge 

signals are clearly very common, they are often low-consequence events, with little or no 

damage to the bridge or equipment. 48.9% 34.6% 5.1% 1.9%

1.8%

2.3%

1.1%

1.0%

0.8%

0.6%

0.3%

0.2%0.2%

0.2%

0.2%

0.9%

0%

10%

20%

30%

40%

50%

60%

8,740 events

Figure 3. Frequency of Industry Bridge-Related Service Interruptions
23

Figure 4 shows the bridge failures in the RBSID from 1999 to 2010. For this comparison, a

bridge failure is considered a total or partial collapse of a bridge. There were 29 bridge failures 

over the 11 years. Hydraulic problems (64 percent), foundation problems (17 percent), and 

failed structural members (17 percent) were the most common causes of bridge failures.

3.4%

17.2% 17.2%

62.1%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Unknown Failed Structural 

Member

Foundation Problems Hydraulic

29 failures over 11 years

Figure 4. Frequency of Railroad Bridge Failures

For comparison, Figure 5 shows the causes of highway bridge failures in the United States from 

1966 to 2005 (39). A similar percentage (60 percent) was due to hydraulic conditions, with 

marine collisions second at 12 percent.
24

Figure 5. Highway Bridge Failures in United States from 1966 to 2005 (presented by 

Briaud – Texas Transportation Institute39)

6.2 Events Resulting in Train Accidents

Events in which a train accident occurs because of a bridge problem represent 5 percent of the 

service interruptions listed in the RBSID. 

6.3 Damage from External Means

It may be useful to separate bridge service interruptions or accidents into those caused by bridge 

deficiencies and those caused by external means. An example of a service interruption caused by 

a bridge deficiency is a condition found during an inspection. Trains may be delayed until 

appropriate action is taken. A common example of a service interruption caused by external 

means is a delay resulting from a bridge strike by a highway vehicle.

The RBSID includes 73 bridges that either failed because of bridge deficiencies or were 

destroyed by external means. Figure 6 shows that more than half of the failures were due to 

external means.
25

Bridge is Victim, 

58%

Bridge deficiency 42% Bridge Caused, 42%

External means 58%

Figure 6. Percentage of Failures because of Bridge Deficiencies and External Means

6.4 Annual Risk Exposure

TTCI developed a simplified model to calculate a risk exposure ranking for each of the identified 

primary hazards. The simplified risk model considers both frequency and severity of loss. Each 

event in the RBSID was assigned a loss value. Next, these values were summed for each 

primary hazard and annualized. Then, the primary hazards were ranked. The hazards with the 

highest exposure were considered as a set of hazards to be considered for bridge monitoring.

6.4.1 Risk Exposure

Actual damage values were available for all of the events from the FRA database. These values 

were modified in several ways:

• First, they were factored for inflation based on the AAR Railroad Cost Recovery Index

(40).

• A multiplier of 1.74 was applied to account for indirect damage. This multiplier was 

developed by AAR to account for clearing wreckage from the track, commodity loss and

commodity damage. This multiplier is updated each year by TTCI as part of the AAR 

Strategic Research Initiatives Program. It is recognized that this average value does not 

account for all possibilities, but it is a first-level attempt to account for these costs. Total 

values are somewhat understated because the multiplier does not include cost of delays, 

traffic diversion, or business loss. 

• Finally, the economic values of a statistical life and injury were accounted for based on 

guidance from the U.S. Department of Transportation (41).
26

Most of the information provided by the railroads did not include costs. Where actual damages 

were not available, general estimates were established.

6.4.2 Estimate of Loss

Each event was assigned a severity category from 1 to 4. Typically, these types of analyses use

more categories, but the available detail in the RBSID does not justify further refinement. 

• Category 1 events are the least serious. They are characterized by negligible damage

with minor service interruption. A frequent example is a bridge strike in which traffic is 

delayed only until an inspection is conducted, and the inspection reveals marginal 

damage.

• Category 2 events result in major damage to the bridge and/or train. Generally, there are 

no injuries, however; significant service interruption occurs.

• Category 3 events are characterized by destruction or collapse of the bridge. These 

include bridge washouts, fires, and severe bridge strikes. There may be injuries involved.

• Category 4 events are the most serious, with both destruction of a bridge and severe 

damage to or loss of a train. There may be injuries and/or fatalities.

An estimate of loss was established for each of the categories. The estimate was based on 

extrapolation of available loss data and input from the industry TAG. A loss of $10,000 per 

event was established for Category 1 events based on the necessity of mobilizing a team to 

inspect and/or make minor repairs and any associated delay costs. Actual damage values were 

available for all of the Category 4 events. 

Categories 2 and 3 events included a wide range of events with widely varying losses. For these, 

order of magnitude estimates were established by averaging available damage values for similar 

events in the FRA database. Estimated losses of $300,000 and $1,500,000 were established for 

Categories 2 and 3 events, respectively; Table 4 shows the basis for the loss values assigned to 

Categories 2 and 3 events. 

Table 4. Basis for Assigned Loss Values 

Severity Average FRA 

Data

Median FRA 

Data

Estimated Loss 

per Event

2 $447,000 $157,500 $300,000

3 $1,806,900 $1,224,200 $1,500,000

Table 5 presents a summary of the category descriptions and costs. Because of the large number 

and limited details associated with the events, there were often overlaps. The authors applied the 

category descriptions in a general way and used judgment as necessary to classify each of the 

events. Severity 1 was assumed if the extent of damage or injuries was not available.
27

Table 5. Description of Severity Categories

Severity Description Examples Loss Estimate

1 Minor service interruption; 

negligible damage.

• Bridge strike – inspection 

reveals negligible damage

• Moveable bridge problems 

because of signal indication

$10,000

2

Major damage to bridge or 

train (significant service 

interruption). Generally, no 

injuries.

• Train derails and 

damages bridge

• Bridge strike requiring repairs

• Defect noted during periodic 

bridge inspection requiring 

extensive repairs

$300,000

3

Bridge collapses or is totally 

destroyed. There may be 

injuries.

• Bridge washed out

• Bridge destroyed by fire

• Severe bridge strike requiring 

bridge replacement

$1,500,000

4

Bridge destroyed with 

severe train damage or loss 

of train; there may be 

injuries and/or fatalities.

• Bridge collapses because of 

scour damage. Train travelling 

over bridge falls in

From FRA 

Safety Database

Table 6 breaks out the source of service interruption data by Severity Category. 

Table 6. Source of Service Interruption Data by Category

Source Category 1 Category 2 Category 3 Category 4 Total

FRA Database 1 126 20 30 177

Railroads 8,047 494 22 0 8,563

Total 8,048 620 42 30 8,740
28

6.4.3 Correction for Missing Data

To present loss estimates on a national basis, a correction factor was established to account for 

missing data. Reasons for missing data include:

• Some U.S. railroads chose not to participate in the investigation

• Some of the participating railroads only provided partial data

• The bridges of one participating railroad are mainly in Canada

The correction factor was based on the total number of railroad bridges in North America and 

their distribution by railroad.

1

 An estimate of the number of the Canadian railroad’s bridges in 

the United States was based on the distribution of their track miles between the United States and 

Canada.

There are a total of about 62,000 Class 1 railroad bridges in the United States. On the basis of

railroad participation, TTCI estimates that the RSIBD contains data for about 32,000 of these 

bridges. This includes the U.S. portions of the participating Canadian railroad. 

The remaining portion of the Canadian railroad’s data was used to replace a portion of the 

missing U.S. data. This increased the total number of bridges represented to about 36,000. This 

total represents about 60 percent of the total number of U.S. bridges.

On the basis of this rough estimate, all estimates of loss were factored to correct for the missing 

40 percent of the data.

6.5 Annual Risk Exposure

Risk exposure values for each event are presented as annual risk. For the FRA data from 1999 to 

2010, the risk exposure was annualized over 11 years. For the railroad data, an appropriate 

period was chosen based on the period for which data were reported.

The RBSID shows that high-consequence events such as the Big Bayou Canot or Kingman, AZ, 

accidents have been very infrequent. None of these events occurred from 1999 through March 

2010. A query over the last 30 years revealed only four of these high-consequence accidents. 

When the annual risk exposure was compiled, these events were included with their cost 

annualized over a 30-year period. 

This simplified approach has several drawbacks. The last high-consequence accident was the 

Kingman Arizona accident in 1997. It may indicate that improved procedures put in place by 

railroads and other entities have reduced the risk. A comprehensive analysis of potential highconsequence events would need to consider not only historical events but also potential events. 

Although methods exist for such an analysis, it is beyond the scope this report.

6.5.1 Ranking of Primary Hazards by Risk Exposure

Figure 7 shows the ranking of primary hazards by annual risk exposure based on the historical 

data assembled. The highest exposure is $25.8 million from Scour/Hydraulic. This is largely 

driven by the 1997 Amtrak derailment in Kingman, AZ. Next in rank is Strike—Marine Traffic. 

This is largely driven by the 1993 Amtrak accident on the Big Bayou Canot Bridge near Mobile,

AL.
29

$0

$5

$10

$15

$20

$25

$30

Millions

Normalized Annual Risk Exposure -- $98 million

Figure 7. Ranking of Primary Hazards by Annual Risk – All Data

Figure 8 shows the ranking of primary hazards by annual risk exposure from 1999 to 2010 only. 

Based on this period, the annual risk is only $72 million. The highest exposure is still from 

Scour/Hydraulic, followed by Strike—Highway Traffic and Damage by Derailed Train. Over 25 

percent of the $98 million from Figure 7 is from the four significant accidents that occurred 

between 1982 and 1997.
30

$-

$3 

$5 

$8 

$10 

$13 

$15 

$18 

$20 

Millions

Normalized Annual Risk Exposure -- $72 million

Figure 8. Ranking of Primary Hazards by Annual Risk – 1999-2010 Data

6.6 Risk Control Matrix

A risk control matrix was developed to match potential problems with existing control measures 

and to identify those areas where additional controls may be warranted. Figure 9 is an excerpt 

from the matrix. Appendix B has the entire matrix.
31

Description of LossHighway Signs, Flashing Lights, Paint, etcBridge LightingBridge Shielding (Fender systems, collision beams)Inner Guard RailTruss Guard RailsCollision Posts (trusses)Annual and Special Inspection (bridge insp)Track InspectorMoveable bridge InspectionMoveable Bridge Tender / Remote Bridge OperatorNDTUnderwater InspectionAutomated Track Inspe VehicleInspection by othersHigh Water DetectorWeather Notification NetworkHigh/Wide Load or Shifted Load DetectorDragging Equipment DetectorOverload/imbalanced Load Detector (OILD)Signal SystemRail Strain MeasurementTrack Displacement DetectorBridge Strike DetectorMid Span DisplacementSelf Diagnostic Moveable BridgesUnattended Scour MonitoringRemote Underwater InspectionBridge Presence IndicationStrain measurementTilt monitorsFire Detection SystemFireproofingVehicle Borne MonitoringPile Displacement Detector

Bridge Strike-Highway Vehicle

Train Accident Due to Undetected Collapse X X X X X O X X O

Repair or Replacement of Collapsed Bridge X X X

Train Derails due to Undetected Damage or Misalignment X X X X X X X X

Repair costs -- Bridge Misalignment/Movement X X X

Repair Costs -- Damage to Substructure/Superstructure X X X

Inspection costs -- no damage x X X

Derailed Train

Repair or Replacement of Collapsed Bridge X X X X X X

Repair Costs -- Damage to Substructure/Superstructure X X X X X X

Scour

Train Accident Due to Undetected Collapse x x X o X X X O o x X X X O X

Repair or Replacement of Collapsed Bridge x X x x X X

Train Derails due to Undetected Damage or Misalignment X X X x X x o X X X X x X x O X

Repair costs -- Bridge Misalignment/Movement x X x X X O X

Repair Costs -- Damage to Substructure/Superstructure x X x x x o X

Bridge Washout

Train Accident Due to Undetected Collapse X X X X O o X O

Repair or Replacement of Collapsed Bridge

Train Derails due to Undetected Damage or Misalignment X X X X X X X X O

Protection Scheduled Inspections Existing Detection Systems Advanced / Prospective Mitiagation Techniques

Figure 9. Excerpt from Risk Control Matrix
32

6.6.1 Primary Hazards

The left column of the matrix lists the primary hazards estimated to have the highest risk 

exposure and the type of loss that would likely result. Potential mitigation techniques or control 

measures are listed in the top row of the matrix. If a control measure is likely to mitigate the 

loss, a mark is put in the cell matching the control measure with the potential loss. An “X” is 

used to indicate a probable match and an “O” is used to indicate a possible match. This process 

provides a quick indication of which types of losses are without controls and which control 

measures will apply to the greatest number of losses.

The 15 primary hazards with the highest risk exposure from Figure 7 are included in the risk 

control matrix. Several potential loss scenarios are associated with each of the primary hazards. 

Loss scenarios can range from inspection costs only resulting from a bridge strike to a worst-case 

event such as a train accident caused by an undetected bridge collapse. These loss scenarios 

were generalized into the 15 potential losses listed in Table 7. The appropriate loss scenarios are 

included in the left column of the risk control matrix with the appropriate primary hazard.
33

Table 7. Potential Losses Due to Primary Hazards

Potential Loss Comments

Train accident caused by 

undetected collapse

Low-frequency/high-consequence—

both the bridge and the train lost

Train accident caused by incorrect 

indication of closed bridge

Repair or replacement of 

collapsed bridge

Train derails due to undetected 

damage or misalignment

Repair costs — bridge 

misalignment/movement

Repair costs — damage to bridge 

substructure/superstructure

Inspection costs — no damage High-frequency/low-consequence

Repairs/delays associated 

with incorrect indication of 

closed bridge

Repairs/delays because of

unidentified track occupancy Result of signal system problems

Repairs delays caused by incorrect 

indication of open bridge

Train derails caused by train 

collision with bridge

Repair costs — damage to 

moveable bridge because of

incorrect operation

Train derails because of track 

defect

Track repair costs

Repair/delay costs—not able to 

open/close bridge
34

6.6.2 Mitigation Techniques

The list of potential mitigation techniques was developed based on consultation with the industry 

TAG. Many of these are described in Section 3. This list may not be comprehensive but 

represents those measures most likely to be considered for implementation. The measures were 

separated into four categories: Bridge Protection Systems, Scheduled Inspections, Existing 

Detection Systems, and Advanced or Prospective Mitigation Techniques

Tables 8–11 list the control measures selected for evaluation from each of the categories.

Table 8. Bridge Protection Systems

Bridge Protection Systems

Highway Signs, Flashing Lights, Paint, etc.

Bridge Lighting

Bridge Shielding (Fender systems, collision beams)

Inner Guard Rail

Truss Guard Rails

Collision Posts (trusses)

Table 9. Scheduled Inspections

Scheduled Inspection

Annual and Special Inspection

Inspection by Track Inspector

Moveable Bridge Inspection

Moveable Bridge Tender/Remote Bridge Operator

NDE

Underwater Inspection

Automated Track Inspection Vehicle
35

Table 10. Existing Detection Systems

Detection System

Inspection by others

High-Water Detector

Weather Notification Network

High/Wide Load or Shifted Load Detector

Dragging Equipment Detector

Weigh-In-Motion for Overloaded Cars/Trucks

Signal System

Rail Strain Measurement

Track Displacement Detector

Table 11. Advanced/Prospective Mitigation Techniques

Mitigation Techniques

Bridge Strike Detector

Midspan Displacement

Self-Diagnostic Moveable Bridges

Unattended Scour Monitoring

Remote Underwater Inspection

Bridge Presence Indication

Strain Measurement

Tilt Monitors

Fire Detection System

Fireproofing

Vehicle Borne Monitoring

Pile Displacement Detector
36

6.6.3 Risk Control Matrix Summary

Figure 10 shows a summary of the risk control matrix results. The bars indicate the number of 

times an occurrence matched a potential loss. A number of conclusions can be drawn:

• Bridge inspection (including annual and special inspection, inspection by track 

inspectors, and inspection by others) is an effective control for many potential losses. 

Currently, inspection is the first line of defense for the railroads.

• There is a large opportunity for defects to be detected by others working on the railway. 

It may indicate that training these individuals to recognize bridge defects may be a costeffective way of reducing losses from bridge accidents and service interruptions.

• Protection systems, where they can be implemented, are likely more effective than 

monitoring.

• Track displacement detectors, tilt monitors, and midspan displacement monitors should 

be considered for additional investigation.

0

5

10

15

20

25

30

Highway Signs, Lights, etc

Bridge Lighting

Bridge Shielding (fender sys, etc)

Inner Guard Rail

Truss Guard Rails

Collision Posts (trusses)

Annual and Special Inspection

Track Inspector

Moveable bridge Inspection

Moveable Brdg Tender / Remote Brdg ...

NDT

Underwater Inspection

Automated Track Inspe Vehicle

Inspection by others

High Water Detector

Weather Notification Network

High/Wide Load or Shifted Load Detector

Dragging Equipment Detector

Overload/imbalanced Load Detector

Signal System

Rail Strain Measurement

Track Displacement Detector

Bridge Strike Detector

Mid Span Displacement

Self Diagnostic Moveable Bridges

Unattended Scour Monitoring

Remote Underwater Inspection

Bridge Presence Indication

Strain measurement

Tilt monitors

Fire Detection System

Fireproofing

Vehicle Borne Monitoring

Pile Displacement Detector

Occurrence

Total "Probable" Total "Possible"

Figure 10. Risk Control Matrix Summary
37

7. Economic Analysis

The estimates of risk exposure developed in Section 6 were used for a preliminary economic 

analysis for 15 potential monitoring systems. First, the database was queried for the bridge 

events that could potentially be mitigated by each potential monitoring system. Actual or 

estimated costs were tallied. The total cost for each system was considered an upper limit of the 

preventable annual risk exposure that the monitoring system might mitigate. Discounted 

cashflow techniques were used on selected monitoring systems to estimate the break-even point 

for each system.

7.1 Upper Limit of Preventable Annual Risk Exposure

The RBSID was queried for the bridge events that could possibly be mitigated by each potential 

monitoring system. Then the risk exposure for each identified event was considered to estimate 

how much might be mitigated by the potential system. Where actual values were available, any

injuries or fatalities as well as any property damage that was related to equipment and track were

included. That is because, in general, the monitoring system would not stop damage to the 

bridge but only the loss from the resulting accident. Where losses were estimated, the entire 

amount was used.

Appendix C includes details for each of the systems considered.

Figure 11 displays the results of the review. Of the 15 monitoring systems considered, seven had 

estimated upper limits between $13.6 and $35.2 million. The remaining eight systems had 

estimated annual upper limits $5.1 million or less. On the basis of these results, the top seven 

monitoring systems were selected for additional evaluation. The selected systems are:

• Track Displacement Detector

• Bridge Strike Detector

• High-Water Detector

• Unattended Scour Monitoring

• Tilt Monitors

• Foundation Displacement Detector

• Weather Notification Network
38

$35.2

$20.6

$15.5 $15.3 $13.9 $13.7 $13.6

$5.1

$2.6 $1.6 $1.2 $0.4 $0.4 $0.1 $0.0

$0

$5

$10

$15

$20

$25

$30

$35

$40

Millions

Figure 11. Potential Preventable Annual Risk Exposure by Technology

The selected monitoring systems included track displacement detectors and tilt monitors, which 

were identified in the risk control matrix as potentially effective mitigation techniques. The 

midspan displacement detector was also identified in the risk control matrix as a potentially 

effective system. However, because estimated preventable annual risk exposure was only 

$0.4 million, it was not selected for further analysis.

7.2 CBA of Selected Monitoring Systems

A discounted cashflow CBA was conducted on six of the seven selected potential monitoring 

systems. 

Although benefits of subscribing to a weather notification system are likely to be substantial, 

detailed analysis is beyond the scope of this investigation. Considerations include:

• Benefits are shared across the entire railroad system.

• Notification of a potentially hazardous condition is not sufficient to prevent a problem. 

Additional action is required, such as sending inspectors to the affected areas.

For the remaining systems, the analysis considered the maximum amount per bridge that could 

be spent on a system. The amount spent could not be greater than the preventable annual risk 

exposure. This can be expressed as follows:
39

Ra ≥ M c

( ) c c c c c c M = f i ,e, fp,m ,o ,u ,c

Where 

Ra = preventable annual risk exposure

Mc = risk mitigation costs

ic = initial cost to include purchase and installation

e = device effectiveness

f p= false positive and reliability issues

mc = maintenance costs

oc = operational costs to include data analysis, communications, etc.

uc = upgrade costs

cc = cost of capital

7.3 Assumptions and Estimations

The following assumptions and estimations were used:

• Because device effectiveness is not known, a parametric approach was used with 

effectiveness considered at 10, 30, 50, and 75 percent. 

• TTCI’s experience with deployment of the Trackside Acoustic Detection System 

(TADS®) was used for a number of estimates. 

─ A false-positive rate of 3 percent of the number of service interruptions was used. 

It was assumed that the cost of a false positive would be the same as a severity 

Category 1 event of $10,000.

─ The initial cost would need to include purchase of the product, installation costs, 

and other associated railroad costs including adding power and communication 

lines.

─ Annual maintenance costs and operation costs combined are estimated at 1 

percent of the installation cost.

─ Upgrades are done every 5 years and are 15 percent of the installation cost. 

(Track displacement detector is not upgraded.) 

─ Life of the detector is 15 years. (Track displacement detector life is 10 years with 

no upgrades at a replacement cost of 50 percent of initial installation.)

The break-even amount was estimated based on a 15-year net present value analysis. A discount 

rate of 11.9 percent was used. This is the rate currently used by AAR and includes allowance for 

inflation. 
40

7.4 Summary of Economic Analysis

The maximum cost per bridge for each implemented technology is highly dependent on the 

effectiveness of the technology, which refers to the percent of the problem that will be prevented. 

For this preliminary analysis, results are presented for 10, 30, 50, and 75 percent effectiveness.

Figure 12 shows the maximum cost per bridge to break even for each of the selected bridge 

monitoring systems. This preliminary analysis assumes that the monitoring system is installed 

on all of the bridges. The track displacement detector has the most promising result. At 50 

percent effectiveness, about $1,600 could be spent per bridge. At 75-percent effectiveness, about 

$2,400 could be spent per bridge. Either the technology would have to be very inexpensive or a 

targeted approach is required.

$-

$500 

$1,000 

$1,500 

$2,000 

$2,500 

$3,000 

Track 

Displacement 

Detector 

Bridge Strike 

Detector 

High Water 

Detector 

Unattended 

Scour 

Monitoring

Tilt monitors Foundation 

Displacement 

Detector 

Max Cost Per Bridge at 100% Implementation

Detector

10% Effectiveness 30% Effectiveness 50% Effectiveness 75% Effectiveness

Figure 12. Maximum Cost per Bridge for Technology to Break even

A large percentage of the Track Displacement detector’s value would be in the reduction of risk 

of derailment resulting from a bridge strike-induced misalignment. In this case, selective 

installation to protect the most vulnerable bridges may be advantageous. Bridges most 

vulnerable to strikes could be identified based on location and history.

As an example, two cases of selective installation are considered. The first case assumes that 

track displacement detectors are fitted on 10 percent of bridges. The second assumes that 

detectors are installed on 25 percent of the bridges. Greater protection may be necessary on 

some lines because of traffic density and difficult operating environment. 

Figure 13 shows maximum cost per bridge for each case, with assumed effectiveness ranging 

from 10 to 75 percent. Assuming that the annual risk is reduced by 50 percent, the maximum 

cost available per bridge would be increased from the $1,600, shown in Figure 12 for installation Maximum Cost per Bridge at 100% Implementation
41

on 100 percent of bridges, to $6,400 if the percentage of installations could be reduced to 25 

percent, and to $24,000 if the percentage of installations could be reduced to 10 percent.

$0

$5,000

$10,000

$15,000

$20,000

$25,000

$30,000

10% 30% 50% 75%

Maximum Cost per Bridge 

to Breakeven

Effectiveness

25% implementation 10% implementation

Figure 13. Maximum per Bridge Cost of Track Displacement Detector 

if Installed on 10 or 25 Percent of Bridges
42

8. Summary

This project was pursued to develop an understanding of the types of bridge problems that cause

accidents or service interruptions and to use this information to evaluate the need to develop new

bridge monitoring systems. Existing monitoring systems and other mitigation techniques were 

also considered, so that efforts can be focused on areas of greatest need.

A literature review was carried out to identify existing and potential monitoring systems and to 

identify similar work that has been undertaken. An industry TAG was formed consisting of chief 

railroad bridge engineers, Volpe, and FRA to provide feedback and direction in the project. The 

TAG was periodically asked to comment on results and to review key assumptions used in the 

study.

Data were gathered from the FRA Safety Database, from railroad databases where available, and 

from interviews with industry experts. Although the FRA Safety Database identifies bridge 

failures, the cause codes do not focus narrowly enough to understand what underlying causes are 

involved. Further, only events above a damage cost threshold and involving train operation are 

included. Unlike the FRA data, railroad data include major events that do not involve train 

operations, such as bridge fires and bridge washouts. In addition, many less serious but frequent 

events are included. However, the railroad data collected varied widely from railroad to railroad. 

Some railroads provided a detailed description of each service delay including the delay time, 

whereas others provided input based on the recollection of key personnel. Both FRA Safety 

Database and railroad data lack detail. Little railroad data older than 10 years is available.

Data from various sources were unified and collated into a useful form in the RBSID. The 

RBSID contains over 8,700 records, including derailments from the FRA Safety Database and 

service interruptions information provided by the five railroads. The database is in Microsoft 

Access to allow for easy entry and query.

Using the available information, a preliminary ranking of hazards based on frequency and 

severity of resulting accidents of service interruptions was carried out. 

Bridge strikes from highway vehicles and problems relating to moveable bridge signals comprise 

the largest number of accidents and service interruptions. Because these are generally lowconsequence events, they may not represent the problems with the largest effect on industry

safety. Table 12 shows the 15 most frequent hazards.
43

Table 12. Top 15 Primary Hazards by Frequency

Primary Hazard Percentage

Strike-Hwy Traffic 48.9%

Moveable Bridge Signals 34.6%

Moveable Bridge Mechanism 5.1%

Damage by Derailed Train 1.9%

Strike-Marine Traffic 1.8%

Scour/Hydraulic 2.3%

Fire 1.1%

Failed Structural Member 1.0%

Defect Found during Inspection 0.8%

Unsafe Walkway 0.6%

Track Geometry/Other Track Defect 0.3%

Foundation Problems 0.2%

Load Shift 0.2%

Earthquake/Tsunami 0.2%

Deterioration- Concrete 0.2%

An analysis that considers both frequency and severity of the events estimates that the annual 

risk exposure from bridge problems is about $98 million. The largest contributor is scour 

combined with other bridge hydraulic problems at about $26 million per year. This is largely 

driven by the 1997 Kingman, AZ, bridge accident. Next in rank is strike from marine traffic at 

about $23 million per year, which is largely driven by the 1993 Bayou Canot accident. Damage 

by derailed trains, fire, and failed structural members follows. Over 25 percent of the $98 

million is attributable to four significant accidents that occurred between 1982 and 1997. Table 

13 summarizes the ranking of hazards by annual risk exposure.
44

Table 13. Summary of Annual Risk Exposure

Primary Hazard Annual Risk 

Exposure (millions)

Scour/Hydraulic $ 25.6

Strike-Marine Traffic $ 22.1

Strike-Hwy Traffic $ 10.2

Damage by Derailed Train $ 8.2

Fire $ 7.2

Failed Structural Member $ 5.5

Moveable Bridge Mechanism $ 4.7

Moveable Bridge Signals $ 4.1

Defect Found during 

Inspection

$ 2.2

Load Shift $ 1.5

Foundation Problems $ 1.3

Broken Rail on Bridge $ 1.3

Track Buckle/Kink $ 0.8

Track Geometry/Other Track 

Defect

$ 0.6

Strike-RR Traffic $ 0.6

Other $ 1.9

Total $ 97.5

A risk control matrix was developed to match potential problems with existing control measures 

and to identify those areas where additional controls may be warranted. Results suggest that:

• Protection systems are likely more effective than monitoring.

• Bridge inspection is an effective control for many potential losses. It is the first line of 

defense for the railroads.

• There is a large opportunity for defects to be detected by others working on the railway,

indicating that training for recognition of bridge defects may be a cost-effective way of 

reducing losses from bridge accidents and service interruptions.

• Track displacement detectors, tilt monitors, and midspan displacement monitors should 

be considered for additional investigation.

The estimates of risk exposure were used for a preliminary economic analysis of 15 potential 

monitoring systems. First, the database was queried for the bridge events that could possibly be

mitigated by each potential monitoring system. Actual or estimated costs were tallied. 
45

Discounted cashflow techniques were used on selected monitoring systems to estimate the breakeven point for each system.

Of the 15 monitoring systems considered, 7 had estimated annual upper limits of preventable 

annual risk exposure between about $24.8 and $9.6 million. The remaining eight systems had 

estimated annual upper limits about $5 million or less. On the basis of these results, the top 

seven monitoring systems were selected for additional evaluation. The selected systems were:

• Track Displacement Detector

• Bridge Strike Detector

• HighWater Detector

• Unattended Scour Monitoring

• Tilt Monitors

• Foundation Displacement Detector

• Weather Notification Network

A discounted cashflow CBA was conducted on six of the seven selected potential monitoring

systems. The CBA considered the maximum initial cost per bridge that could be spent on a 

system based on the preventable annual risk exposure. Results indicate that for implementation 

of any of the systems to be cost-effective, a selective implementation strategy would be required. 

Across-the-board implementation would not be cost-effective. Additional work is recommended 

to design a structured, risk-based approach for selective implementation of monitoring systems.
46

9. Recommendations

Results have indicated that the annual risk exposure from bridge related events is nearly $100 

million. Preventable annual risk exposure over $36 million could be attributed to certain 

detectors. However, because of the large number of railroad bridges in service, results indicate 

that for implementation of any of the systems to be cost-effective, a selective implementation 

strategy would be required. Across-the-board implementation would not be economical. 

A second phase of work is a proposed development of a risk assessment method to identify those 

bridges that will give the best return for having remote monitors installed. A comprehensive 

analysis of potential high-consequence events would need to include development of a structured 

approach to consider the possibility of events that have not been documented historically. The 

work would likely require one or more moderated meetings of experts to evaluate potential 

bridge-related problems that may represent risks to personnel or equipment. A deliverable for 

this work could include a computer program to help bridge owners determine which of their 

bridges should be considered for monitoring.

The literature review and the analyses reported here indicate that good bridge inspections are the 

first and last line of defense against bridge failures. Service interruptions due to defects found 

during inspections accounted for over $2 million in annual risk exposure. This indicates that 

scheduled inspections are identifying problems before they cause operational problems. Because 

inspections are an integral and successful part of maintaining bridge safety and reliability, 

additional work is proposed to identify technologies that can aid the inspection process. This 

might include improved NDE techniques of bridge health monitoring technologies.

Railroads would be surveyed to identify the types of problems that are being found during 

inspections. Bridge inspectors and other industry experts would be interviewed for an overview 

of needs to be addressed. Current and potential technologies would be identified.

An FHWA program to introduce new bridge inspection technologies is discussed in this report. 

The program identified a suite of five of the latest relatively inexpensive, portable, techniciandriven NDE technologies to aid bridge inspectors. FHWA developed a one-day seminar to 

familiarize bridge inspectors with these technologies. The FHWA effort should be consulted for 

the applicability of the identified technologies for railroad applications and for the methods used 

to identify the five technologies. Deliverables for this work could include a short seminar similar 

to the one developed by the FHWA.

Railroads should consider development of training courses for track inspectors and others on 

identification of bridge hazards.
47

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51

Appendix A. 

Risk Control Matrix
52

Figure A1. Risk Control Matrix Page 1
53

Figure A2. Risk Control Matrix Page 2
54

Figure A3. Risk Control Matrix Page 3
55

Appendix B. 

Preventable Annual Risk Exposure for Selected Systems

Service interruptions included in the potential preventable risk exposure per are shown in 

Tables B1-B12. Note that the total potential preventable risk exposure per year value is not 

corrected for missing data.

Table B1. Track Displacement Detector

Year Primary Hazard Number of Injuries Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

1982 Other Hydraulic-Bridge 15 0 $699,838

1993 Strike-Marine Traffic 103 47 $14,540,6504

1997 Other Hydraulic-Bridge 183 0 $8,069,557

1999 Track Buckle/Kink 0 0 $297,568

2000 Track Buckle/Kink 0 0 $25,867

2000 Other Hydraulic-Bridge 0 0 $112,509

2001 Track Buckle/Kink 0 0 $109,936

2002 Bridge Misalignment 0 0 $49,739

2003 Track Buckle/Kink 0 0 $13,452

2003 Track Buckle/Kink 0 0 $8,358

2003 Track Buckle/Kink 0 0 $44,179

2003 Hydraulic-Approach 0 0 $11,181

2005 Track Buckle/Kink 0 0 $9,689

2005 Other Hydraulic-Bridge 0 0 $20,131

2006 Track Buckle/Kink 0 0 $5,306

2007 Hydraulic-Approach 0 0 $ 5,800

2007 Other Hydraulic-Bridge 2 0 $729,456

2007 Bridge Misalignment 0 0 $18,873

2007 Strike-Hwy Traffic 0 0 $1,709

2008 Track Buckle/Kink 0 0 $47,974

Total $24,821,775
56

Table B2. Bridge Strike Detector

Year Primary Hazard Number of

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

1993 Strike-Marine Traffic 103 47 $14,540,650

Total $14,540,650

Table B3. High Water Detector

Year Primary Hazard Number of

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

1982 Other Hydraulic-Bridge 15 0 $694,656

1997 Other Hydraulic-Bridge 183 0 $7,962,202

2000 Other Hydraulic-Bridge 0 0 $14,351

2002 Other Hydraulic-Bridge 0 0 $3,857

2002 Other Hydraulic-Bridge 1 0 $113,058

2003 Scour 0 0 $3,218

2005 Other Hydraulic-Bridge 0 0 $15,623

2007 Scour 0 0 $17,110

2007 Other Hydraulic-Bridge 2 0 $560,494

2008 Other Hydraulic-Bridge 0 0 $85,715

2008 Scour 0 0 $105,938

2008 Other Hydraulic-Bridge 0 0 $11,349

Total $9,587,576
57

Table B4. Unattended Scour Monitoring

Year Primary Hazard Number of

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

1982 Other Hydraulic-Bridge 15 0 $699,837

1997 Other Hydraulic-Bridge 183 0 $8,069,557

2000 Other Hydraulic-Bridge 0 0 $112,509

2002 Other Hydraulic-Bridge 0 0 $59,431

2002 Other Hydraulic-Bridge 1 0 $139,733

2003 Scour 0 0 $110,491

2005 Other Hydraulic-Bridge 0 0 $20,131

2007 Scour 0 0 $17,110

2007 Other Hydraulic-Bridge 2 0 $729,456

2008 Scour 0 0 $223,098

2008 Other Hydraulic-Bridge 0 0 $605,436

2008 Other Hydraulic-Bridge 0 0 $51,332

2008 Other Hydraulic-Bridge 0 0 $51,332

Total $10,889,453
58

Table B5. Tilt Monitors

Year Primary Hazard Number of

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

1982 Other Hydraulic-Bridge 15 0 $694,656

1997 Other Hydraulic-Bridge 183 0 $7,962,202

1999 Foundation Problems 0 0 $16,891

2000 Other Hydraulic-Bridge 0 0 $14,351

2001 Failed Structural Member 0 0 $795

2001 Foundation Problems 0 0 $1,120

2001 Foundation Problems 0 0 $14,466

2002 Other Hydraulic-Bridge 0 0 $3,857

2002 Other Hydraulic-Bridge 1 0 $113,058

2003 Scour 0 0 $3,218

2003 Foundation Problems 0 0 $42,288

2004 Failed Structural Member 0 0 $84,949

2005 Other Hydraulic-Bridge 0 0 $15,623

2005 Foundation Problems 0 0 $5,049

2006 Foundation Problems 0 0 $17,116

2006 Foundation Problems 0 0 $8,863

2007 Scour 0 0 $17,110

2007 Other Hydraulic-Bridge 2 0 $560,494

2007 Failed Structural Member 0 0 $11,445

2007 Foundation Problems 0 0 $5,739

2008 Scour 0 0 $105,938

2008 Other Hydraulic-Bridge 0 0 $85,715

2009 Failed Structural Member 0 0 $12,655

Total $9,797,596
59

Table B6. Foundation Displacement Monitoring

Year Primary Hazard Number of

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

1982 Other Hydraulic-Bridge 15 0 $694,656

1997 Other Hydraulic-Bridge 183 0 $7,962,202

2000 Other Hydraulic-Bridge 0 0 $14,351

2001 Foundation Problems 0 0 $1,120

2002 Other Hydraulic-Bridge 0 0 $3,857

2002 Other Hydraulic-Bridge 1 0 $113,058

2002 Foundation Problems 0 0 $27,787

2003 Scour 0 0 $3,218

2005 Foundation Problems 0 0 $5,049

2005 Foundation Problems 0 0 $162

2005 Other Hydraulic-Bridge 0 0 $15,623

2006 Foundation Problems 0 0 $17,116

2006 Foundation Problems 0 0 $8,863

2007 Scour 0 0 $17,110

2007 Other Hydraulic-Bridge 2 0 $560,494

2007 Foundation Problems 0 0 $5,739

2008 Other Hydraulic-Bridge 0 0 $85,715

2008 Scour 0 0 $105,939

Total $9,642,058
60

Table B7. High Wide Shifted Load

Year Primary Hazard Number of 

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

1999 Load Shift 0 0 $5,530

1999 Load Shift 0 0 $172,710

1999 Damage by Derailed Train 0 0 $85,121

2000 Load Shift 0 0 $69,284

2000 Load Shift 0 0 $2,878

2000 Damage by Derailed Train 0 0 $14,866

2000 Load Shift 0 0 $55,220

2001 Load Shift 0 0 $95,313

2001 Damage by Derailed Train $27,273

2001 High/Wide Rail Carload 0 0 $7,053

2002 High/Wide Rail Carload 0 0 $2,223

2002 Load Shift 0 0 $185,376

2002 Damage by Derailed Train 0 0 $217,937

2002 Damage by Derailed Train $27,273

2003 Damage by Derailed Train 0 0 $163,450

2003 Load Shift 0 0 $2,000

2003 Load Shift 0 0 $234,448

2003 High/Wide Rail Carload 0 0 $1,537

2003 Damage by Derailed Train 0 0 $20,935

2003 Damage by Derailed Train 0 0 $114,615

2003 Load Shift 0 0 $8,510

2004 Damage by Derailed Train $136,364

2004 Damage by Derailed Train 0 0 $5,739

2004 Damage by Derailed Train 0 0 $121,292

2005 Damage by Derailed Train 0 0 $500,145

2005 Damage by Derailed Train 0 0 $215,494

2005 Damage by Derailed Train $27,273

2005 Damage by Derailed Train $27,273

2005 High/Wide Rail Carload 0 0 $6,312

2005 Load Shift 0 0 $26,148

2006 Damage by Derailed Train 0 0 $84,195
61

Table B7. High Wide Shifted Load (continued)

Year Primary Hazard Number of 

Injuries

Number of 

Fatalities

Potential Preventable 

Risk Exposure per Year

2006 Damage by Derailed Train 0 0 $12,723

2006 Load Shift 0 0 $7,035

2007 Damage by Derailed Train $136,364

2007 Damage by Derailed Train $27,273

2007 Damage by Derailed Train $27,273

2007 Damage by Derailed Train $27,273

2007 Load Shift 0 0 $3,687

2007 Load Shift 0 0 $23,952

2007 Damage by Derailed Train $27,273

2007 Load Shift 0 0 $33,554

2007 Load Shift 0 0 $17,804

2007 Load Shift 0 0 $41,176

2008 Damage by Derailed Train $136,364

2008 Damage by Derailed Train $27,273

2008 Damage by Derailed Train 0 0 $129,107

2008 Damage by Derailed Train $27,273

2008 Strike-RR Traffic $27,273

2009 Damage by Derailed Train $136,364

2009 Damage by Derailed Train $27,273

2009 Damage by Derailed Train $27,273

2009 Damage by Derailed Train $27,273

2009 Damage by Derailed Train $27,273

Total $3,641,910
62

Table B8. Rail Strain Measurement

Year Primary Hazard Number of

Injuries

Number of 

Fatalities

Potential Preventable 

Risk Exposure per Year

1999 Track Buckle/Kink 0 0 $276,203

1999 Broken Rail on Bridge 0 0 $55,548

2000 Track Buckle/Kink 0 0 $17,808

2001 Track Buckle/Kink 0 0 $38,880

2003 Track Buckle/Kink 0 0 $10,745

2003 Track Buckle/Kink 0 0 $4,822

2003 Track Buckle/Kink 0 0 $37,313

2005 Track Buckle/Kink 0 0 $590

2005 Broken Rail on Bridge 0 0 $15,155

2005 Broken Rail on Bridge 0 0 $39,393

2005 Broken Rail on Bridge 0 0 $29,615

2005 Broken Rail on Bridge 0 0 $28,672

2006 Track Buckle/Kink 0 0 $685

2006 Broken Rail on Bridge 0 0 $97,631

2007 Broken Rail on Bridge 0 0 $32,699

2009 Broken Rail on Bridge 0 0 $140,687

Total $826,446
63

Table B9. Mid Span Displacement Detector

Year Primary Hazard Number of

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

1999 Failed Structural Member 0 0 $9,859

2001 Foundation Problems 0 0 $1,120

2001 Failed Structural Member 0 0 $795

2001 Foundation Problems 0 0 $14,466

2002 Foundation Problems 0 0 $27,787

2003 Scour 0 0 $3,218

2003 Foundation Problems 0 0 $42,288

2004 Failed Structural Member 0 0 $84,949

2005 Foundation Problems 0 0 $5,049

2005 Failed Structural Member 0 0 $39,393

2006 Foundation Problems 0 0 $17,116

2006 Foundation Problems 0 0 $8,863

2007 Foundation Problems 0 0 $ 5,739

2007 Failed Structural Member 0 0 $11,445

2009 Failed Structural Member 0 0 $12,655

Total $284,741

Table B10. Strain Monitoring

Year Primary Hazard Number of

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

2004 Failed Structural Member 0 0 $84,949

Total $84,949
64

Table B11. Fire Detector

Year Primary Hazard Number of

Injuries

Number of

Fatalities

Potential Preventable 

Risk Exposure per Year

2009 Fire 0 0 $635,508

2009 Fire 0 0 $56,143

2010 Fire 1 1 $1,131,245

Total $1,822,896

Table B12. Vehicle Borne Monitoring

Year Primary Hazard Number of 

Injuries

Number

Fatalities

Potential Preventable 

Risk Exposure per Year

1999 Foundation Problems 0 0 $16,891

1999 Failed Structural Member 0 0 $9,859

2001 Failed Structural Member 0 0 $ 795

2001 Foundation Problems 0 0 $1,120

2001 Foundation Problems 0 0 $14,466

2003 Foundation Problems 0 0 $42,288

2004 Failed Structural Member 0 0 $84,949

2005 Foundation Problems 0 0 $5,049

2005 Failed Structural Member 0 0 $39,393

2006 Foundation Problems 0 0 $17,116

2006 Foundation Problems 0 0 $8,863

2007 Failed Structural Member 0 0 $11,445

2007 Foundation Problems 0 0 $5,739

2009 Failed Structural Member 0 0 $12,655

Total $270,626
65

Abbreviations and Acronyms

AAR Association of American Railroads

AREMA American Railway Engineering and Maintenance and Way Association

BNSF Burlington Northern Sante Fe

CBA cost-benefit analysis

CP Canadian Pacific

FHWA Federal Highway Administration

FRA Federal Railroad Administration

GIS geographic information system

LTBP Long-Term Bridge Performance

MNDOT Minnesota Department of Transportation

NDE nondestructive evaluation

NS Norfolk Southern

RBSID Railroad Bridge Service Interruption Database

TADS® Trackside Acoustic Detection System

TAG technical advisory group

TRB Transportation Research Board

TTCI Transportation Technology Center, Inc.

UP Union Pacific

Volpe John A. Volpe National Transportation Systems Center