Covered Bridge 

Security Manual

Brent Phares

Terry Wipf

Ryan Sievers

Travis Hosteng

Forest

Products

Laboratory

General 

Technical 

Report

FPL–GTR–223

United States Department of Agriculture

Forest Service

In cooperation 

with the

United States

Department of

Transportation

Federal 

Highway 

Administration
May 2013

Phares, Brent; Wipf, Terry; Sievers, Ryan; Hosteng, Travis. 2013. Covered 

bridge security manual. General Technical Report FPL-GTR-223. Madison, 

WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 34 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53726–2398. This publication is also available online at 

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries 

in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin. 

The use of trade or firm names in this publication is for reader information 

and does not imply endorsement by the United States Department of 

Agriculture (USDA) of any product or service.

The USDA prohibits discrimination in all its programs and activities on the 

basis of race, color, national origin, age, disability, and where applicable, 

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and employer.

Abstract

The design, construction, and use of covered timber bridges 

is all but a lost art in these days of pre-stressed concrete, 

high-performance steel, and the significant growth both in 

the volume and size of vehicles. Furthermore, many of the 

existing covered timber bridges are preserved only because 

of their status on the National Registry of Historic Places 

or the diligent maintenance and care of the owners of these 

structures, or both. Of the covered timber bridges that 

remain in the United States, only a small percentage still 

stand today because of arson, vandalism, neglect, natural 

disasters, and other factors. The objective of this work is 

to provide covered timber bridge owners with the tools to 

quickly and efficiently design and implement a security 

system to protect these important historical landmarks. This 

goal was obtained with an in-depth analysis of equipment 

based on the practicality in a covered bridge application. 

Other major considerations required for all equipment to 

work efficiently within a security system are also fully 

discussed, including, but not limited to, maintenance, power 

requirements, and general set-up of an integrated security 

system. A comprehensive case study is presented involving monitoring systems placed on five of the six covered 

bridges in Madison County, Iowa, at the end of this report 

to showcase the abilities of an integrated system and all the 

decisions that must be made throughout the process for the 

entire system to work as intended.

Keywords: Covered bridges, wood bridges, security

Contents

Introduction.........................................................................1

Overview—Covered Bridge Surveillance Project, 

Iowa State University..........................................................1

Literature Review................................................................2

Covered Bridge Monitoring System: Design......................5

Set-Up ...............................................................................17

Testing...............................................................................19

Summary...........................................................................20

Recommendations.............................................................20

Madison County Project ...................................................21

Challenges with Each Bridge............................................24

Testing...............................................................................29

Example Case Studies.......................................................29

Real Case Studies..............................................................31

References.........................................................................33

This study is part of the Research, Technology and Education portion of the National Historic Covered Bridge 

Preservation (NHCBP) Program administered by the 

Federal Highway Administration. The NHCBP program 

includes preservation, rehabilitation and restoration of 

covered bridges that are listed or are eligible for listing 

on the National Register of Historic Places; research for 

better means of restoring, and protecting these bridges; 

development of educational aids; and technology transfer 

to disseminate information on covered bridges in order to 

preserve the Nation’s cultural heritage.

This study is conducted under a joint agreement between 

the Federal Highway Administration–Turner 

Fairbank Highway Research Center, 

and the Forest Service – Forest Products Laboratory.

Federal Highway Administration Program Manager– 

Sheila Rimal Duwadi, P.E.

Forest Products Laboratory Program Manager– 

Michael A. Ritter, P.E.
Covered Bridge Security Manual

Principal Investigator

Brent Phares

Co-Director, National Center for Wood Transportation Structures

Institute for Transportation, Iowa State University

Co-Principal Investigator

Terry Wipf

Co-Director, National Center for Wood Transportation Structures

Institute for Transportation, Iowa State University

Research Assistant

Ryan Sievers

Travis Hosteng

Bridge Research Specialist, Bridge Engineering Center

Institute for Transportation, Iowa State University

Introduction

Covered bridges used to cover the American landscape from 

coast to coast. However, because of various factors including neglect, arson, vandalism, and natural disasters, currently less than 700 to 900 bridges are still in existence today. 

Covered bridges tend to be in isolated areas, and they are 

constructed with a flammable material, which makes them 

highly susceptible to arson and vandalism. Because they are 

usually far from populated areas, it is difficult for firefighters to arrive at the bridges in a timely manner once a fire has 

been set. This makes it likely that any fire may cause critical 

damage or may completely destroy a bridge. Most of these 

covered bridges are covered by volunteer fire departments, 

which only adds another level of complexity to the situation. 

It is essential that we protect and preserve these standing 

landmarks throughout our country for future generations. 

One way to provide the necessary security is to use remote 

monitoring and other security systems to protect them from 

trespassers.

Multiple bridge owners throughout the United States have 

taken measures to ensure the safety and integrity of their 

covered bridges by implementing structural strengthening, 

fireproofing, and monitoring systems. Common protective 

methods entail illuminating the bridge site and using fireretardant material around important structural members. 

These methods are typically used because they are usually 

very cost effective. Unfortunately, these systems are passive 

approaches and provide no mechanisms to alert the proper 

authorities and increase the chances of survival for the 

bridges.

This report is intended to assist covered bridge owners in 

selecting systems that will protect covered bridges with the 

option of adding active alerts to proper authorities for the 

purpose of heightening security. Because very little technical literature exists dealing exclusively with the subject of 

security and monitoring systems for covered bridges, we 

contacted multiple Departments of Transportation (DOTs) 

with a high concentration of covered bridges as well as 

multiple bridge owners to assess the state of covered bridge 

security in the United States. This insight from bridge owners coupled with technical literature about physical security 

of other assets is the basis of this report.

Overview—Covered Bridge 

Surveillance Project, Iowa State 

University

In 2005, the Bridge Engineering Center (BEC) at Iowa State 

University (ISU) completed a case study on remote security 

of historic covered bridges by designing and implementing 

an active monitoring system on the Cedar Covered Bridge in 

Madison County, Iowa (Phares 2006). The security system 

installed on the Cedar Bridge is discussed further in the case 

studies portion of this report. The work completed and the 

system developed for the Cedar Bridge resulted in the BEC 

receiving a grant from the Federal Highway Administration 

(FHWA), through the National Historic Covered Bridge 

Preservation Program (Matias 2011), to install remotely 

monitored security systems on the other five covered bridges 

in Madison County. The five bridges included in the security 

monitoring grant, the Cutler–Donahoe, Holliwell, Hogback, 

Imes, and Roseman covered bridges, are five of the six landmark bridges that remain in Madison County and the only 

bridges that have not been completely rebuilt. The Hogback 

Bridge was partially damaged by arson but managed to survive and was restored to its original condition one year after 

the incident. The Cedar Bridge, made famous by the book, 

The Bridges of Madison County by Robert James Waller, 
General Technical Report FPL–GTR–223

2

was completely destroyed by arson in 2002 but rebuilt to 

original specification in 2003–2004 (Overington 2003).

For the Cutler–Donahoe, Holliwell, Hogback, Imes, and 

Roseman bridges, we decided to design a basic system with 

a high degree of functionality that could be tailored to fit the 

majority of covered bridge sites encountered rather than to 

design a security system to be specific to a given bridge site. 

The developed security system includes two flame detectors, 

an infrared camera, an optical camera, and multiple pieces 

of communication equipment necessary to relay all the information back to the design team as well as to officials in 

Madison County. We were required to install an alternative 

energy system at the Hogback Bridge site because it is so 

distant from local grid power. An in-depth analysis of the 

security system for these five bridges and problems encountered can be seen later in this report.

The implementations in Madison County were not completed to show what every covered bridge monitoring system 

should entail. Rather, they provided a mechanism to showcase different ideas, constraints, and limitations for designing a surveillance system for other bridges. This manual is 

intended to showcase the most predominant and functional 

technology in the area of surveillance and monitoring at the 

time of its preparation.

Scope of Work

This manual is intended to provide covered bridge owners with a tool to aid in the development and deployment 

of security strategies. The research team has completed an 

extensive government literature review at the local, state, 

and Federal levels, which included contacting several DOTs 

and local governments with a high concentration of historic covered bridges that have installed, or are planning to 

install, security systems or other preventative measures on 

their bridges. Multiple companies that specialized in outdoor security systems were contacted to define cutting-edge 

technologies in the security industry at the time this report 

was written. Note that this manual is not intended to be an 

all-inclusive list of possible security system equipment 

and tactics, but a guide to best practices, techniques, and 

equipment.

Literature Review

Pertinent Covered Bridge Literature

Very little information related to the security of covered 

bridges has been published. As a result, the majority of the 

information summarized here deals with general security of 

bridges or general asset security.

Although there is a lack of published literature dealing 

exclusively with covered bridges, numerous professionals 

throughout the country have substantial knowledge related 

to covered bridges. When possible, these professionals were 

contacted to provide additional information. 

The Beginning of Covered Bridges 

in the United States

The first covered bridges in the United States appeared in 

the Eastern states in the early 1800s and thereafter were 

constructed across the country until the early 1900s when 

steel bridges became a more economical choice for bridge 

construction. Covered bridges built during this period were 

built to reflect the architectural style of a specific time and 

place while still being a functional and vital passageway for 

the community. Numerous builders and architectural styles 

created unique structures that personified communities 

around the country.

As years passed, the covered bridge became a romanticized 

icon of the United States of the 1800s. As bridge and road 

design became routine and repetitive, the distinctive architecture of the past started to stand out more and more when 

compared with its modern counterpart. Although new construction of covered bridges ceased around the turn of the 

20th century, they were still used well into the new century 

and many continue to be renovated and repaired for use today and well into the future. Despite the best efforts to preserve the bridges at the turn of the 20th century, many covered bridges were lost to neglect, fire, flooding, and other 

disasters both natural and manmade (Becker 2011).

Different statistics vary about how many covered bridges 

were constructed and how many still stand today. However, 

it is clear that a relatively small percentage still stand today 

when compared with the turn of the 20th century. Recently, 

the Federal government as well as multiple state and local 

governments have placed significant emphasis upon preserving our covered bridges. This is evident by the allocations 

in governmental budgets for spending on covered bridge 

preservation. Many bridge owners are currently installing 

security systems to provide protection against arson and 

vandalism or plan to do so.

Structural Integrity

The bridges were covered for several different reasons. 

Many historians believe it was to give the appearance that 

the bridge was a barn and this would have a calming effect on farm animals as they crossed waterways that would 

otherwise startle them. People also believe that that the 

bridges were covered to protect travelers who were caught 

in inclement weather or to hide people on romantic strolls. 

These ideas may have been considered by the builders when 

putting coverings on their bridges; however, the main reason 

that bridges were covered was for a more practical and functional reason. Designers felt that by covering the heavy 

and expensive trusses from direct rainfall and sunlight, 

the life expectancy of the bridge could be extended. The 

designers were correct; history has proven that a covered 

bridge will last up to three times longer than a similar noncovered bridge. Although the sacrificial wall and roof cover-
Covered Bridge Security Manual

3

ings would have to be replaced every couple of decades, it 

was still a more economical choice than completely replacing the bridge or structural trusses in the same time frame. 

The ability to extend the life of timber truss bridges by using 

sacrificial wall and roof coverings was discovered early in 

the age of bridge design in Europe and other parts of the 

world and was an integral part of timber bridge concepts 

when it arrived in North America (Becker 2011).

Targeting Covered Bridges: Arson 

and Vandalism

Experts estimate that over 176,000 intentional outdoor fires 

are set by arsonists every year. These fires result in approximately 20 deaths, 250 injuries, and $23 million in losses 

annually according to Volume 9, Issue 6 of the Topical Fire 

Report Series (National Fire Data Center 2009). Out of all 

the outdoor fires that occur every year in the United States, 

27% are intentionally set by arsonists (National Fire Data 

Center 2009). Arson is a prevalent problem in the United 

States that destroys property and life and must be addressed 

in a serious manner. Intentionally set outdoor fires tend to be 

more common in the spring from March and April and once 

again in mid-summer, especially July 3–5, according to the 

National Fire Incident Reporting System (NFIRS). Because 

these are the times when arson is most likely to occur, it is 

recommended that, at a minimum, the highest level of security be active during these time 

periods.

The devastating effects of arson are evident when committed on covered bridges in small towns all over the country. 

Unfortunately, this kind of damage is prevalent throughout 

recent history as seen in Indiana (Rinehart 2005), Iowa 

(Overington 2003), and Pennsylvania (Murphy 2008). The 

number of covered bridges throughout the United States is 

quickly dwindling because of arson as well as neglect. On 

average, over the last 20 to 30 years, two to three bridges 

apparently have been set on fire with one or two of these 

bridges being completely destroyed, as shown in Table 1. It 

is essential that cities and states that own and maintain covered bridges take the proper measures to ensure that these 

bridges will survive for future generations to enjoy.

Indiana

In 2005, a fire destroyed one of the 31 covered bridges remaining in Park County, Indiana. The Bridgeton Bridge was 

beloved by all in the area and was known as the most photographed bridge in the county before the fire. A 35-year-old 

male, who was a person of interest in an arson case with 

another covered bridge in the area, seemingly poured an accelerant across the length of the bridge and ignited it sometime around midnight. Both of the bridges were completely 

destroyed and collapsed. A few months prior to these arson 

cases, firefighters were able to save another bridge, which 

also appeared to be intentionally set on fire (Rinehart 2005).

Iowa

Madison County, Iowa, is well known for its covered 

bridges because of the popularity of the 1992 book, The 

Bridges of Madison County, and the 1995 movie adaption with leading actors Clint Eastwood, Meryl Streep, and 

Annie Corley. None of the six remaining covered bridges in 

the county were made as popular by the book as the Cedar 

Bridge, which is on the cover of the book and is a central 

bridge throughout the entire story. On September 3, 2002, 

the Cedar Bridge was completely destroyed by arson, only 

4 years after over $128,000 was invested in restoration. The 

town was extremely distraught over the loss of the bridge, 

given the large amount of tourism it brought to the community and the manner in which it was destroyed. This prompted the city to replace the structure with an exact replica with 

as similar of construction techniques as possible the next 

year (Overington 2003).

Table 1. Bridge fires (1992–2002)

Year Bridge name Comments 

1992 Loy's Station 

1992 Parker Survived 

1993 Slate Bridge 

1993 Jordan 

1993 Corbin 

1993 Smith 

1993 LeMay Ferry 

1993 Nectar C.B. 

1993 Sells 

1993 Kilgore Mill 

1994 Wolf Bridge 

1994 Grimes 

1994 Guilford 

1994 Kaufman's Distillery 

1994 Upper Sheffield 

1995 Miller Road Survived 

1996 Wimer Survived 

1996 Carman 

1997 Offult Ford 

1997 Lower 

1997 Wilkinson 

2000 Henniger Farm Survived 

2001 Pine Grove Survived 

2002 Ryot Bridge 

2002 Orne Bridge 

2002 River Road 

2002 Cedar Bridge 

2002 Henderson Survived 

2002 Risser's Mill 

2002 Jackson Survived 

2002 Jeffries Ford 

2002 Woodsville Survived 

2002 Newfield Survived 

2002 Wilson's Milla Survived a

Wilson’s Mill Covered Bridge (Avella, 

Pennsylvania) is thought to have survived 

because of a metal deck. 
General Technical Report FPL–GTR–223

4

Pennsylvania

One of the three remaining bridges in Erie County, 

Pennsylvania, was set ablaze in December 2008 by two 

local men. The destruction of this particular bridge was 

damaging to the city for two separate reasons. The historic 

Gudgeonville Covered Bride in Girard Township was valued 

at over $1 million and was of great importance to local tourism and also a vital part of the roadway system that still carried traffic over the Elk Creek. Both of the men responsible 

for these crimes were suspects in other crimes throughout 

the area including burglary, criminal trespass, and theft that 

are all unrelated to the bridge incident (Murphy 2008).

Although arson is a major problem throughout the United 

States, especially when it pertains to covered bridges, several steps can be taken to reduce the chances of trespassers 

committing destructive acts toward the covered bridge. In 

this report, we discuss several successfully implemented 

recommended procedures for covered bridge security 

around the United States. With care and diligence, the probability that arson and vandalism will occur on a particular 

bridge can decrease significantly.

Importance of Historical Integrity

It cannot be stressed enough that any modifications completed on covered bridges including security systems or 

any other type of rehabilitation must be completed with 

the greatest of care to ensure that the historical significance 

of the covered bridge is preserved. The National Register 

of Historic Places has strict guidelines as to what will and 

will not be accepted as a historical place. To be eligible for 

some funds from government agencies to preserve a covered 

bridge, it is important that a covered bridge is on the register 

of historic places before and after any modifications. The 

National Register of Historic Places has strict criteria that 

must be met for all historic places. It is important that all 

bridge owners be aware of these criteria before embarking 

on any project in, on, or around a covered bridge.

Listing in the National Register of Historic Places provides 

formal recognition of a property’s historical, architectural, 

or archeological significance based on national standards 

used by every state. Benefits include the following:

•	 Becoming part of the National Register Archives, a public, searchable database that provides a wealth of research 

information.

•	 Encouraging preservation of historic resources by 

documenting a property’s historic significance.

•	 Providing opportunities for specific preservation 

incentives, such as

o Federal preservation grants for planning and 

rehabilitation

o Federal investment tax credits

o Preservation easements to nonprofit organizations

o International Building Code fire and life safety code 

alternatives

•	 Possible state tax benefit and grant opportunities.

•	 Involvement from the Advisory Council on Historic 

Preservation when a Federal agency project may affect 

historic property.

Physical Security of Structures

Physical security is a basic principle necessary for the survival of any person, place, or object. Throughout history, 

people have used security to protect their privacy, property, 

and lives whether it be with a weapon, by constructing large 

impenetrable walls, or more recently by using cameras or 

other monitoring devices to detect and apprehend ill-willed 

individuals. By definition, security means the freedom from 

danger, fear, or anxiety (Merriam Webster Dictionary). By 

this definition alone, security covers a wide array of areas 

including information, physical, political, and monetary, as 

well anything that requires protection from danger. To some 

degree, there is a concept of security dealing with almost 

all areas of life, which makes it difficult to cover security in 

depth at all levels.

Structures can come under attack from terrorism, sabotage, 

natural disasters, and other threats that may be unique to 

a particular area. It is essential when designing a security 

system for a certain structure that a full analysis is done 

to ensure that the level of security required is obtained. 

Designing a security system for any structure is always a 

case of planning for unknown dangers in type and magnitude, with the understanding that not all security risks and 

dangers can be prevented, deterred, or even detected.

Numerous security measures can be taken for all types of 

structures whether it be a bridge, building, or any other type 

of asset. Many of these types of security will not transfer 

from one type of structure to another. A building, for example, may be under a high level of security by only allowing traffic through approved entrances and restricting all 

unwanted entry through physical barriers or alarm systems 

or both. Although the ability to completely monitor all traffic going through and around the structure is ideal for almost 

all applications, it is not necessarily the most feasible. This 

is especially true for bridges, which are designed to allow 

traffic to flow easily. Security measures that require stopping and checking all modes of transportation using the 

bridge would prove to be uneconomical and unreasonable. 

However, many precautions and security measures may be 

implemented to greatly increase the security of the structure 

and decrease the probability of dangerous behavior 

occurring.

Blue Ribbon Panel Workshop on Bridge 

and Tunnel Security

In 2003, the FHWA organized a Blue Ribbon Panel (BRP) 

Workshop on Bridge Security Assessments following the 
Covered Bridge Security Manual

5

terrorist attacks of September 11, 2001, to analyze the safety 

of the transportation infrastructure (DOT 2003). The BRP 

was given the objective to “Develop short- and long-term 

strategies for improving the safety and security of the nations’ bridges and tunnels, and provide guidance to highway infrastructure owners/operators.” The BRP decided 

upon five major levels of security to construct an effective 

defense against unwanted activities on or toward bridges. 

These levels include 1) deter, 2) deny access, 3) detect presence, 4) defend the facility, or 5) design structural hardening 

to minimize consequences to an accepted level. The BRP 

report goes into detail about designing structural hardening 

but does not go into much detail about the other four areas.

Although all levels of security are not equally discussed 

in full detail within the BRP report, the research team felt 

it was prudent to investigate and discuss all five levels of 

security in greater detail. By considering all five levels of 

security when developing a security system for a bridge or 

any other structure, the owner is able to assemble a system 

that is not only effective, but redundant, and that provides 

the greatest level of security possible for the given budget. 

Within this report, the concept of structural hardening is 

covered only briefly as several different publications look 

at structural hardening of bridges and covered bridges in 

particular. This report’s main goal is to complement these 

publications with the other four main portions of security 

discussed within the BRP’s assessment. Below, these four 

levels are briefly discussed; furthermore, multiple examples 

of each of the areas are discussed within the equipment 

options portion of this report.

Deter

Deterrence is prevention or discouragement of a detrimental action by means of fear or doubt. For the case of bridge 

security, the fear created would be that anyone who would 

commit detrimental actions to the bridge would be caught 

and prosecuted. One of the more inexpensive options for 

deterrence would be to place signs around the bridge, alerting all visitors that surveillance equipment and alarms are 

implemented on site, and local authorities will be alerted of 

any trespassers after hours. Quite simply, the presence of 

this type of sign creates fear or doubt (whether or not the 

surveillance equipment actually exists or not).

Greater levels of deterrence can be implemented if the designer of the security system believes that the bridge is more 

susceptible to arson or vandalism. For example, in extreme 

situations, deterrence by means of onsite security personnel 

may be warranted. Additional levels of increased security 

may include lighting, barricades, or alarm systems placed 

such as to frighten any trespassers off the premises. In some 

cases, the goal of these measures is, quite simply, to create a 

sense of uncertainty and fear about a particular site.

Deny

Denying trespassers access to the bridge site is one of the 

more difficult portions of the security program laid out by 

the BRP. Because most covered bridges are in secluded 

areas, trespassers may enter the site several different ways. 

Many of the methods used for deterrence can also be able 

to deny trespassers to a limited degree. The use of fences 

and barricades around the bridge area could deny, or at least 

slow down, potential threats to the bridge.

Detect

In the case of arson and vandalism, surveillance of the 

bridges is a great first step in the detection. An added benefit is that, once detected, other steps can be taken to lessen 

the probability of total destruction of the bridge, as will be 

discussed further. Much of the equipment discussed in this 

report pertains to the detection of threats. The detection of 

threats can be an invaluable portion of many security systems. This detection of threats is important because it facilitates alerting local authorities if there is anything going on 

at the bridge site.

Defend

The ability for the covered bridge to defend itself once a 

fire has been started can be essential for the survival of the 

bridge. There are multiple ways to defend a bridge such as 

sprinkler systems or the application of fire-retardant paint 

or wood during construction or renovation. Defense is fundamentally different from structural strengthening, as the 

addition of defensive measures does not change the bridge 

in a structural sense but only protects the existing structure 

from fire.

Education

Although all of these physical security measures are important to ensure the highest level of security at a covered 

bridge, the importance of education should never be overlooked when discussing preventative measures against arson 

and vandalism. By educating the public in areas surrounding 

a covered bridge about its historical significance and the importance of preserving the structure, awareness of the bridge 

is increased and those who take interest in a sense become 

added security to the bridge. This can easily be done by 

placing articles in local newspapers, going to local middle 

and high schools to discuss the history of covered bridges, 

posting signs, and many other options.

Covered Bridge Monitoring 

System: Design

Preliminary Decisions

Multiple decisions must be made to deploy an effective security system that can fulfill the needs and desires of each 

bridge owner. Some of these main decisions are discussed 

in detail within this section; however, these decisions and 

discussions may not be all inclusive, and proper discretion 

should be used when implementing a covered bridge security system. Illustrated in Figure 1 are some of the more 

major decisions that go into designing a security system. 
General Technical Report FPL–GTR–223

6

Subsequent sections provide more detail regarding the information and terms presented in Figure 1 to give the designer 

a more detail for each part of the system.

All equipment or components that are used on or around 

the bridge site must be carefully selected so that they do not 

detract from the aesthetic value of the bridge and are able to 

survive in a hostile environment, all the while providing acceptable levels of performance with minimum maintenance. 

These criteria prove to be the most important aspects of any 

equipment choice for most covered bridge applications. All 

components of the security system that are located on the 

bridge site should be weather resistant, resistant to the constant abuse of insects or animals, and be placed so that the 

components themselves are protected from vandalism. An 

in-depth look measures the need to protect equipment and is 

discussed in further detail in the set-up section of this report.

All the following equipment explanations are designed to 

be a brief overview and not a complete narrative. Multiple 

sources exist such as online reviews and other publications 

that can assist the security system designer when selecting 

equipment options based upon their abilities and limitations. 

Detailed communication with all equipment manufacturers 

can ensure that all devices can be integrated effectively and 

meet or exceed the requirements of the bridge owner.

Equipment Options

Each covered bridge is unique in its aesthetics, structural 

design, and surrounding landscape, so equipment may be 

listed here that would not be applicable to a specific bridge. 

The designer of the security system for a particular bridge 

should be sensible and rational about what pieces of equipment are selected. In later sections of this report, we discuss 

which systems might be best used for different locations and 

situations.

None of the equipment listed below is intended to be used 

stand-alone to protect a structure. Several pieces of equipment that work together to protect the bridge need to be integrated as efficiently as possible. The five areas of security 

that are listed by the BRP (i.e., deter, deny, detect, defend, 

and strengthen structure) cannot be obtained with a single 

piece of equipment. Any one piece of equipment may only 

provide one or possibly two types of security; therefore, to 

obtain optimal levels of security, it is essential to use multiple pieces of equipment that have multiple abilities, 

as shown in Figure 2.

A decision-making tool, shown in Figure 3, was created to 

aid bridge owners in making quick decisions about the type 

of security system to be installed on a particular bridge with 

a given budget. All prices are considered to be average and 

may be significantly higher or lower depending on the abilities of the equipment and the specific manufacturer. Each 

piece of equipment that is listed in this spreadsheet is expanded upon in this section with capabilities and limitations 

of all equipment. 

Deterrence Equipment

Alarm System—Any of the above pieces of security equipment, either stand-alone or together in a system, are nothing 

more than hardware without the integration of a carefully 

designed alarm system. Chapter 104, Tyska and Fennelley 

Preliminary decisions

Box Grid power

Detection

Structure

Remote destination

Equipment Pole placement Enclosures Power

Deter

Deny

Defend

Functionality

Aesthetics

Renewable energy

Figure 1. Equipment options.
Covered Bridge Security Manual

7

(2000) discusses alarm systems in great detail. Several different alarm systems may be used depending on the intent 

and level of security. The different types of systems can 

include alarms that silently send out an alarm to the proper 

authorities, a system that emits an audible alarm, some type 

of visual alarm in the area of the bridge, or a combination of 

the two. Several different issues may factor into the decision 

on what type of alarm system to use, such as the bridge’s 

proximity to local authorities and residential areas. If the 

bridge is in close proximity to a residential area, it may not 

be attractive to have a loud, audible alarm that could disturb 

residents for all alarms, real and false. The proximity to the 

local authorities, and more specifically their response time, 

is also a key factor in the decision of the type of alarm system. If the bridge is within a reasonable distance to a fire 

department or police station, it may be more appropriate to 

have a silent alarm that will only alert the local authorities 

and give them the possibility of apprehending the criminal. 

If there is more considerable distance between the bridge 

and the local authorities or if the bridge is protected by a 

volunteer fire department, an audible alarm may alert both 

the criminal and nearby local public with the intent of 

deterring the criminal before more damage is inflicted to the 

structure.

A standard alarm system generally consists of the following:

•	 Detection elements located at the protected area, designed 

to initiate alarm upon entry of an intruder.

•	 Transmission lines that conduct signals to a device in the 

immediate area or to a central annunciator panel that can 

be continuously monitored.

•	 A panel that announces by visible or audible signals the 

structure or area in which an alarm has been activated.

•	 Fail-safe features that provide a signal at the annunciator 

panel if any part of the system is malfunctioning.

Lighting—Most vandalism and arson are committed during 

the nighttime hours because the trespassers are disguised by 

the darkness. Adequate lighting at the bridge site at all times 

can prove to a cost effective and efficient way of protecting the bridge. In Chapter 24, Tyska and Fennelley (2000) 

discuss lighting and note the importance of using the right 

amount of lighting that is effective yet does not contribute to 

Equipment selection flowchart for covered bridges

Infrared camera

Video surveillance

Heat detector

Smoke detector

Flame detector

Fiber optic sensor

Alarm system Fire hydrant

Sprinkler system

Fire retardant material

Barricades

Lighting Fences

Signage

Deter Deny Detection Defend

Alarm system

Figure 2. Flow chart of equipment options.
General Technical Report FPL–GTR–223

8 Equipment Average Price ****Threat Level Average Capabilities Main Drawbacks *Requirements Maintenance

Alarm System MA/MV Audible/Visible signals at structure Notify proper authorities Possibility of false alarms at bride site Can notify trespasser and allow excape Low electrical draw Enclosure for communication Monthly

Annunciator Panel $300

Lighting $70/fixture MA/MV Make portions of bridge site visible day/night Allow cameras to see during low light levels Can lead to light pollution Moderate electrical draw Yearly

Signage $50 LA/LV Inform trespassers of consequences Rare

Barricades $300 LA/MV Limit traffic to certain sized vehicles Stop traffic altogether from entering bridge May be difficult to move when necessary Rare

Decorative Planters $300 Rare

Bollards $150 Rare

Fences $15/foot LA/MV Limit access points at bridge site Cannot completely limit access points Rare

Chain Link $8/foot Rare

Wood $10/foot Rot and warping of wood may occur over time Yearly

Wrough Iron $25/foot Rare

Block Wall **$10/SF Rare

Infrared Camera $5,000 HA/LV Monitor temperatures within field of view View bridge regardless of amount of light False alarms due to glare, animals, or heat Sensitive to environment High electrical draw Pole Yearly

Video Surveillance $300 LA/MV View bridge during times of adequate light Allow remote parties to view bridge Dependent on lighting in field of view High electrical draw Pole Yearly

Heat Detector $100 HA Monitor temperatures around detector False alarms due to environment Moderate electrical draw Yearly

Smoke Detector $50 MA Monitor smoke levels around detector Highly vulnerable to exterior conditions Low electrical draw Monthly

Flame Detector $1,500 HA/LV Monitor temperatures within field of view False alarms due to glare, animals, or heat Moderate electrical draw Yearly

Fiber Optic Sensor MA Monitor temperatures along length of device Possible difficult with installing Moderate electrical draw Yearly

Fire Hydrant **$3,000 MA Provide water source to fire department Requires close water supply Close water supply Yearly

Sprinkler System **$15,000 HA Extinguish fires started within interior of bridge Requires close water supply Bulky and not aesthetically pleasing Close water supply Yearly

Fire Retardant Material $8/SF HA Stop or slow the ignition of a fire Stop the spread of any fires that may start Loss of effectiveness over time Loss of structural strength to applied members Every few years

Intumescent Coating $8/SF

Fire Retardant Wood ***%20 increase

 MV: Medium Vandalism HV: High Vandalism LA: Low Arson MA: Medium Arson HA: High Arson

Deter Detection

Notes:*** 20% increase from typical lumber used on covered brdges****Protection from Different Threat Levels LV: Low Vandalism

Deny

* Draw requirements are as follow Low: 0.01 - 0.2 amps AC  Moderate: 0.25 - 0.49 amps AC High: 0.5+ amps AC** Includes installation

Defend

Figure 3. Equipment selection tool.
Covered Bridge Security Manual

9

any light pollution, which could be unattractive and costly. 

Many guidelines can be used to limit light pollution on 

the bridge site including the use of sensors, timers, highefficiency fixtures, directional fixtures, and others. It may 

also be more economical in the long run for a professional 

with experience with exterior lighting to design the lighting system. Proper lighting can be used in unison with an 

optical camera to improve effectiveness. Multiple types of 

lighting can be used in a variety of situations. They include 

the following:

Perimeter Lighting: This type of lighting is used to illuminate the fence or perimeter of a certain site. The perimeter 

for covered bridge sites could be at a certain distance 

from the bridge or be the perimeter of the bridge itself. 

Perimeter lighting is used so that trespassers must pass 

through an adequately lit perimeter that may or may not 

be under surveillance. This is to act as a deterrent to the 

trespassers.

Area Lighting: This type of lighting is used to illuminate 

the area immediately surrounding the bridge that must be 

passed through to enter the bridge. Much like perimeter 

lighting, area lighting is used as a deterrent to trespassers 

by making it necessary for people to pass through brightly 

lit areas to reach the bridge.

Floodlighting: Floodlighting is used to saturate an entire 

area with bright lighting to deter trespassers. This type of 

lighting may detract from the aesthetics of the bridge and 

distract people driving by and living near the bridge site.

Gatehouse Lighting: This type of lighting illuminates 

entrances and exits to and from the site. This is essential 

for the entrances of both sides of the bridge as well as entrances to major roadways around the bridge site.

Signage—Placing signage around the entrances of the 

bridge site stating that anyone who enters after nightfall or 

attempts to deface the bridge will be prosecuted to the fullest extent of the law is an effective way of deterring trespassers. Signage stating that there is a surveillance system 

on site that is running 24 hours a day should also be considered for added deterrence. The more signage that is present 

on the site, the more likely it is that people entering the site 

will see it. In Chapter 89, Tyska and Fennelley (2000) discuss the usage of signage in great detail.

Deny Equipment

Barricades: In Chapter 4 of Perimeter Security, Michael 

Arata (2006) discusses barricades in full detail. Many 

covered bridges today are closed to motor vehicles to 

reduce live loads on the bridge. Barricades offer a variety 

of advantageous features. Foremost is that they make it 

difficult for trespassers to get too close to the bridge with 

motor vehicles. This is important, as this means that they 

must travel distances on foot, which may slow entry to the 

site, and more importantly, exit after a defacement has occurred. There are several different barrier options including natural and man-made styles.

Natural Barriers: The bridge owner does not have much 

influence on the types of natural barriers present at a 

given bridge site. In most cases, these types of barriers 

cannot be moved or changed in any major way because of 

physical limitations, aesthetics, or environmental regulations. Thus, the security system designer should seek to 

leverage the natural barriers to enhance the security at the 

site and minimize any negative influence they may have 

on the system. Many different types of natural barriers 

will be unique to every bridge site. Examples of possible 

natural barriers that may be present at any given site are 

as follows:

•	 Rivers―Many covered bridges were used to span 

over rivers, so this will be a typical natural barrier that will occur at many bridge sites unless the 

bridge was moved to a safer location. Rivers are an 

effective way of keeping trespassers away from the 

shielded and vulnerable underside of the bridge.

•	 Thick brush―Much like rivers, some covered 

bridges are in heavily forested areas where vegetation will be close to the bridge site. Some may 

consider this to be a nuisance, but thick brush can 

act as a natural barrier that will keep out motor vehicles and, in many cases, trespassers. The security 

system designer can choose to plant hedgerows in 

strategic areas to deny or deter trespassers from 

entering certain areas of the bridge including underneath the bridge itself.

•	 Mountains―Some bridges may be in mountainous 

areas where sheer rock walls or other features can 

be present around the bridge site. Sudden changes 

in elevation can aid the security system, as many 

trespassers would be deterred by having to climb a 

large shear wall or incline.

Man-Made Barriers: As mentioned earlier, several different options for barriers can be chosen by the security 

system designer. Some options may not be reasonable at 

all sites but some possible options for man-made barriers 

are as follows:

•	 Decorative planters―The use of decorative planters can take multiple shapes whether it is as a 

planter or a bench. The main advantage of using 

a decorative planter is that they are aesthetically 

pleasing and can be an efficient barrier. They will 

deter motor vehicles from entering the bridge site 

but can be temporarily moved by a forklift or other 

heavy machinery in the event that someone with 

authority needs to enter the bridge for maintenance 

or other legitimate reasons.
General Technical Report FPL–GTR–223

10

•	 Bollards―A bollard is a cylindrical tube that is 

usually 12 to 24 in. in diameter and can have variable heights above the ground (Fig. 4). The many 

types of bollards include fixed, removable, and retractable, and they can be constructed from a wide 

range of materials including wood, concrete, steel, 

or plastic. 

•	 K-rail―Also commonly known as a Jersey barriers because they were first used on the New Jersey 

Turnpike, K-rails are typically used to deflect motor vehicles safely. K-rails are sometimes viewed as 

not very aesthetically pleasing (Fig. 5).

•	 Welded steel guard rails―Much like the K-rail, 

the use of welded steel guardrails may not be the 

preferred choice because of its negative aesthetic 

value. Although it may have not been aesthetically 

pleasing, the use of steel guardrails is generally a 

low-cost and effective way to protect the entrance 

to bridges.

•	 Berms/ditches―One of the simplest ways of creating a barrier is to simply have a ditch or berm 

around an area that is off limits (as long as it does 

not create a hydraulic scour hazard). This may 

not be as effective as other means, as some motor 

vehicles may be able to navigate over or around a 

ditch or berm.

Fences: In Chapter 3 of Perimeter Security, Michael 

Arata (2006) discusses fences in full detail in the book. 

Fences at a bridge site would help to force the public to 

enter the bridge site through secure entrances that can be 

monitored and controlled. Fences should not be considered to be a way of completely preventing unwanted entry 

into a bridge site but rather a way of slowing down and 

deterring trespassers.

When deciding to build a fence, many decisions need to 

be made, depending on the type of bridge site that is being 

secured, including the following:

•	 Chain Link—Chain link fences are the most common type of perimeter fences because of their 

price, easy set-up, and low maintenance requirements. The chain link fence is so functional that 

the Federal government widely uses it and has 

the following specifications that can be found in 

Federal Standard RR-F-191/1A. The following is a 

summary of Federal specifications taken from the 

Defense Logistics Agency (DLAI 5710.1):

1. Fabric made of chain link

2. No. 9 gauge or heavier wire

3. Seven feet high

4. Fence fabric mounted on metal posts set in 

concrete

5. Mesh openings not larger than 2 in2

6. Fence bottom within 2 in. of solid ground

7. Fence top guard strung with barbed wire, and 

angled outward and upward at a 45-degree angle

8.The fabric used for the chain link fence should 

be galvanized, aluminized, or plastic-coated woven steel. The fabric should be connected to the 

posts with the same gauge wire that the fabric 

itself is made out of. If a fabric is used that has 

openings larger than 2 in2, then the fence itself 

will be much easier for intruders to climb and 

should be avoided when possible. The use of 

privacy slats are commonly used with chain link 

Figure 4. Typical bollards. Figure 5. Standard K-rail (Permission to reprint given by 

Rob Vander Veen, Mid State Concrete Products, Santa 

Maria, CA). 
Covered Bridge Security Manual

11

fences but should be avoided on bridge sites as 

they allow intruders the ability to approach the 

fence without detection from the outside.

The Federal specifications are not required by 

bridge owners but are good guidelines for creating an effective perimeter. The use of barbed 

wire for extra security may not be required, as 

most bridge sites will not need this high level 

of security.

•	 Wrought Iron—The wrought iron fence is growing in popularity but is used mainly as an upgrade 

to chain link fences. Wrought iron fences are used 

commonly in residential areas as they are more 

decorative and aesthetically pleasing. The top of 

the fence is typically bent toward the outside of 

the area being contained with the ends sharpened 

for added security. It can be more difficult to climb 

a wrought iron fence than a chain link fence, especially a chain link fence without barbed wire, 

but the added cost of a wrought iron fence may be 

prohibitive.

•	 Wood—There are many options when using wood 

fences including design and level of security. Most 

wood fences do not allow a clear line of site to the 

other side of the fence, which is not desirable on a 

bridge site. With this lack of vision and the increase 

in maintenance required when compared with steel 

fences, wood fences are not typically a viable option for bridge sites.

•	 Concrete or Block Wall—Much like the wood 

fence, when using concrete or block walls many 

options can be considered as each wall is unique 

(e.g., type of block, color of block, type of foundation). Many concrete walls have barbed wire 

installed on top for added security, but this is not a 

requirement. Concrete or block walls will generally 

be significantly more expensive than a steel fence 

and will take longer to install.

Detection Equipment

Infrared Camera: An IR camera has the ability to detect 

and record the temperatures of different elements within 

its field of view during all times (e.g., during daytime and 

night time). This key attribute of IR cameras makes them 

especially attractive, as most acts of arson and vandalism 

occur during at night when the perpetrator can be masked 

by darkness. The major drawback for installing an IR 

camera at a bridge is the inherent cost when compared 

with other surveillance equipment.

IR cameras with appropriately configured software have 

the ability to detect motion and to issue alarms at certain 

temperature thresholds, and certain rates of temperature 

change. Great care should be taken when using a motion 

detection device of any type as large animals, such as 

deer or bears, could enter the field of view of the camera 

and set off the motion detector resulting in a false alarm. 

In general, however, these problems can be overcome 

by properly setting the “person” detection temperature 

threshold properly. Another threshold temperature setting 

issue relates to the type of wood preservative used on the 

bridge. Specifically, it has been observed that timber treated with creosote can get hot enough to approach flame 

temperatures and can thus cause false alarms.

As mentioned earlier, the main negative associated with 

IR cameras is the initial purchase price. Since IR camera 

technology is more advanced than other surveillance 

equipment, it might be more costly. As a result, the designer must consider if the advantages of deploying IR 

camera technology warrants the initial cost.

Typically, IR cameras are not built for exterior applications so it is important to include weather-resistant, 

protective housing for the cameras when estimating the 

system cost. Many such enclosures are offered by the IR 

camera manufacturer and can be custom made for any sort 

of application (including internal heating, internal cooling, etc.). Although the cost is high, it is still a valuable 

piece of equipment and was used on multiple case study 

bridges detailed later on in this report.

Video Surveillance—Video surveillance equipment is viable 

for monitoring bridge activity during the daytime or if the 

bridge is adequately lit during nighttime hours. It is important to know the technical abilities required of the camera 

and to choose a camera that will meet or exceed the expectations. The price for a common video surveillance camera 

is quite low and it may prove appropriate to place multiple 

cameras around a site.

Some cameras have the ability to change from infrared to 

visible light depending on the level of light in its vicinity. 

These cameras may be a more economical decision than 

buying them both separately. There are several manufacturers of cameras for adverse exterior conditions that range in 

ability and price. It is important to work with the manufacturer to select the appropriate camera for the bridge site in 

question. Much like the IR camera, the video surveillance 

camera must be located in a tamper resistant and environmentally appropriate housing.

Heat Detector—Several different types of heat detectors can 

be selected for bridge security. The two most common heat 

detectors commercially available are the fixed temperature 

and the rate of rise heat detectors. The fixed temperature 

heat detector is set to sound an alarm once a predetermined 

temperature has been reached. A rate of rise heat detector 

will set off any alarm once a certain rate of temperature gain 

has been reached. Both the predetermined temperature and 

rate of rise can be adjusted. In many ways, these settings are 

relatively the same as the IR camera thresholds mentioned 

earlier.
General Technical Report FPL–GTR–223

12

Note that the rate of rise heat detector may be more vulnerable to false alarms within the given environment. 

Specifically, covered bridges may be susceptible to sudden 

increases in temperatures, such as being warmed by the sun 

or a piece of machinery operating next to or on bridges that 

are still open to traffic. With these conditions being present 

on most covered bridges, it is important to place heat detectors out of direct sunlight. Some possible places to put these 

devices would be underneath the wooden deck or underneath the rafters on the top portion of the bridge.

Smoke Detector—A smoke detector may assist with fire 

protection coverage on a covered bridge; however, it may 

have a higher source of false alarms because the smoke 

detector will have to be placed within the covered bridge to 

be effective and will be vulnerable to dust and other debris 

coming in contact with it. In general, most smoke detectors 

are not designed to operate outdoors and special care must 

be given if a bridge owner wishes to deploy such a monitoring device.

Flame Detector—A flame detector may be one of the more 

important pieces of equipment in a set-up for security of 

covered bridges. The flame detector may be placed within 

the bridge interior where it will be able to view a large portion of the bridge. If necessary, multiple flame detectors 

may be used together in a system to optimize coverage of 

the bridge. Most flame detectors have a mechanism that significantly reduces false alarms

In general, flame detectors rely upon multiple measurements 

to determine if a fire has been set. First, and probably most 

obviously, flame detectors detect heat and are generally preprogrammed to know typical flame temperatures. Further, 

flame detectors typically have a sensing component that detects the unique flicker rate of flames. These redundant systems tend to reduce the number of false alarms that occur.

Fiber Optic Sensor—Fiber optic sensors may be used to 

measure rotation, acceleration, electric and magnetic field 

measurement, temperature, pressure, acoustics, vibration, 

linear and angular position, strain, humidity, viscosity, 

chemical measurement, and a host of other sensor applications not mentioned here. The fiber optic sensors typically 

used for bridge security measure changes in temperature 

along the length of the bridge. The main advantage of these 

sensors is that they have good bandwidth size and are lightweight, small, passive, resistant to electromagnetic interference, highly sensitive, and durable.

Many different types of fiber optic cables vary in price 

and it is important to choose a cable that can survive in the 

adverse exterior conditions where many of the bridges are 

located. The cost of fiber optic cables can be very cheap 

when compared with other equipment, and the cost continues to go down as the technology improves. However, the 

hardware required to read the fiber optic sensors tends to be 

quite expensive.

Defend Equipment

Fire Hydrant—One portion of fire protection that could easily be overlooked is how the fire will be extinguished. Fire 

trucks can store their own water and some even have the 

capability of pumping water from sources such as nearby 

rivers and lakes. However, in some cases the water source is 

too far below the elevation of the road to allow pumping. In 

this case, an additional pump at the water may be necessary 

to aid the fire truck in pumping the water up to the road elevation. It is important to know the limitations and abilities 

of the fire department that provides service to the covered 

bridge of interest.

If a municipal source exists near the structure, fire hydrants 

should be located on both sides of the bridge placed at a far 

enough standoff distance that heat from a bridge fire would 

not impede fire fighters hooking up hoses. If it is uneconomical to connect to the municipal water source because of the 

isolated condition of the covered bridge, it may be plausible 

to install a dry fire hydrant by connection to a water source 

nearby, as mentioned above.

Sprinkler System—If a fire of considerable size has been established before the fire department can arrive at the bridge, 

the center of the bridge may be inaccessible to fire personnel. This is a major problem for the structural integrity of 

the bridge, as this is where some of the largest forces exist. 

This problem can be solved by the installation of sprinkler 

systems within the center portion of the bridge or along the 

entire length of the bridge. It is essential that the sprinkler 

system selected be a dry pipe system so that freezing and 

bursting pipes do not become a problem during inclement 

weather. A dry pipe system has no water in the pipes until a 

sprinkler head is set off, at which point water enters the system and extinguishes the flames.

The first question the bridge owner would ask when discussing the possibility of installing a sprinkler system is the 

aesthetic effect on the bridge. As most sprinkler systems 

are relatively bulky and unattractive, it is important to place 

them in inconspicuous areas that are not seen by the public. 

The most economical and effective areas to place the sprinkler systems would be running underneath the bridge with 

the flow pointing upward toward the bridge deck and above 

the roofing members with the direction of the flow pointing 

down and to the sides. This will provide the greatest bridge 

coverage for most bridge applications.

Fire-Retardant Material—Achim Hering (2001) gives us 

insight on fire-retardant materials in The Proof Is in the Fire.

One of the most common types of security measures taken 

by covered bridge owners is to increase the fire resistance 

of the bridge. This is due to the cost efficiency of the material when compared with the level of protection added to the 

bridge. This can come in the form of some sort of coating 

such as intumescent coating or using fire-retardant wood 

when rehabilitating or repairing a bridge. This falls under 
Covered Bridge Security Manual

13

the category of structural strengthening and will help the 

bridge stay structurally sound during the course of a fire before it is able to be extinguished. Using fire-retardant materials should not be seen as a final solution for bridge security 

because they do not stop the initiation of a fire but slow the 

progress of a fire such that major damage can be avoided. 

The application of a fire-retardant material to structural elements that are essential to the survival to the bridge is one of 

the most desired actions with bridge security related to fires.

Many of the lighter bridge elements such as shingles, siding, 

and any thinner wooden framing should be considered when 

deciding what needs to be treated with fire-retardant materials. These thinner pieces can be ignited much easier than 

the larger structural members such as the bridge deck and 

primary truss members. These thinner bridge elements can 

be the fuel required to ignite the larger members and cause 

serious structural damage in the case of a long-burning fire. 

Although it may be more economical and efficient to make 

the thinner elements fire retardant, it is not uncommon to 

make the entire structure fire retardant for an added level of 

fire safety. The cost should be weighed against the advantage of such an extensive procedure.

Intumescent Coating—One of the more common fireretardant materials used for covered bridges is intumescent 

coating. Intumescent coating is a thin layer of material very 

similar to paint in method of application as well as aesthetics and texture. It can come in a variety of colors including 

clear and semi-clear. There are multiple manufacturers of 

intumescent coatings and similar materials that can match 

the exact color scheme of any bridge so this coating can be 

applied to existing or new bridges.

The way intumescent coating works is by swelling when exposed to a certain level of heat that would be seen during the 

course of a fire. The chemically bound water in the coating 

absorbs heat, making it ideal for fireproofing applications. 

Intumescent coatings are used to keep the fire in the location 

of its origin instead of spreading. This type of coating will 

only become active after being exposed to heat. Although 

the coating of essential structural members is the most important, it is also beneficial to coat the entire bridge including siding, roofing, and all framing.

Although this is a very effective method of making a structure more fire resistant, it still has several drawbacks that 

must be considered for optimum protection. Much like any 

coating, intumescent coating will break down and become 

less effective over time and will need touch ups every few 

years and possibly an entirely new coat after multiple touch 

ups. These times are dependent on the conditions at the 

bridge site including humidity, direct sunlight, and temperature changes. Different manufacturers will have different 

materials that will be adaptable to different conditions so 

it is important to choose the correct coating for an exact 

bridge location.

Fire-Retardant Wood—Robert Durfee (2003) has an extensive section on fire-retardant wood in his article, “Vermont’s 

Covered Bridges.” Fire-retardant wood is created by 

pressure-treating the wood with a fire-retardant chemical. 

Multiple manufacturers of fire-retardant materials use different chemicals and have differing levels of fire resistance. 

Most fire-retardant woods are designed to not light on fire 

even with direct contact with a flame or the fire will not 

spread after it is initially lit.

A major drawback to using fire-retardant wood is the decrease in the structural strength of the member by up to 10% 

to 20% depending on the exact type of chemical used. This 

can become a major issue if fire-retardant wood is used on 

structural members such as the bridge deck, as the members may need to be larger since they will have decreased 

strength. Much like the intumescent coating, there is a decline in the effectiveness of fire-retardant wood that is accelerated from being in a harsh exterior location. This decline 

in effectiveness can be slowed substantially by painting the 

wood soon after installing it.

Pole Placement

Most security systems, especially those involving cameras, 

will be required to have a pole or pedestal of some kind for 

placement of the necessary security monitoring hardware. 

Below are some of the key factors to consider when selecting a pole type and location.

Aesthetics

The pole placement will ultimately be a decision directed by 

owner of the bridge and the security system designer. The 

most important factor influencing the final placement of the 

pole will be the aesthetic effect on the area surrounding the 

bridge while at the same time being placed so that adequate 

coverage is achieved. Because covered bridges can be a 

major source of tourism for smaller towns around the United 

States, it is important that the security systems installed do 

not draw attention away from the bridge and the surrounding landscape. Depending on the landscape and surroundings, this may be detrimental to the effectiveness of the 

security system because this usually requires that the pole be 

placed a large distance away from the bridge. An ideal situation at the bridge location would be a pre-existing pole such 

as a light pole or power line pole that, upon approval of the 

owner, could double as the mounting pole.

The type of material used for the pole is mostly an aesthetic 

decision. Several different types of materials can be used 

for the pole such as metal, concrete, or wood. To blend in 

with the surrounding area, we suggest that a survey be taken 

of what is around the possible pole location to see if other 

light or electrical poles are within sight. If other poles are 

in the surrounding area, it would be preferable to use the 

same type of material and pole height to let the security pole 

blend into its surroundings.
General Technical Report FPL–GTR–223

14

Line of Site—Even if a pole is within a reasonable distance 

from the bridge, it must be guaranteed that there is a direct 

line of sight to both the front and rear entrances to the bridge 

to allow the system to be as efficient as possible. Even if 

there is a direct line of sight at the moment that the security system is enabled, it is important to look for possible 

obstructions in the future such as trees or other vegetation 

that could have the potential to grow or move into the direct 

line of sight. Any potential problems should be dealt with as 

soon as possible to avoid costly problems in the future.

It may be possible to only allow a direct line of site to one 

entrance of the bridge because of environmental constraints. 

If the designer has the ability to use a pole facing toward 

either entrance of the bridge, many criteria must be considered. If the bridge is closed to vehicle traffic, then the 

entrance that will see the greatest amount of pedestrians 

would likely allow for the greatest amount of security on the 

bridge. The ease of connecting to electrical power should 

also be considered if electronic equipment will be used in 

the security system.

Functionality—Placing the pole at a significant distance 

from the bridge creates multiple problems, and there must 

be a compromise between aesthetics and functionality to 

make the pole as practical as possible while still keeping 

its presence as benign as possible. The two major problems 

with placing the pole at a significant distance from the 

bridge come from the effectiveness of the cameras and problems associated with running the wire over long distances. 

Both of these problems can be solved by using more sophisticated equipment; however, doing so directly correlates to 

an increased cost for the project.

A camera is still effective in generating a clear and usable 

image at differing ranges. These ranges will obviously 

change with differing manufacturers and cameras, and it is 

important to be cognizant of all camera specifications to ensure that all limitations at a certain bridge are overcome by 

the camera selected. This is applicable to all cameras used 

on the bridge including infrared or optical cameras.

The other problem that results from a greater pole distance 

is functionality losses within the wires that must be run from 

the pole to the bridge. Although this particular problem will 

not usually be a critical problem with the security system 

design, it needs to be considered before placing the system 

in the field to ensure that the proper power is reaching the 

systems. If this is done, the system will operate as expected 

and will result in fewer maintenance issues in future. If major problems with power loss occur across the wire between 

the bridge and the pole, several different solutions could be 

applicable, depending on the amount of power loss. One 

solution could be to use a wire with a higher conductivity so 

there would be less loss. Another solution could be to use a 

higher source of power that will overcompensate for the loss 

across the wire.

It may desirable to the owner to use the pole for other functions outside of security reasons. These other functions 

could include placing a street light on the top of the pole to 

provide lighting for the surrounding area. This could also be 

considered a security device, as well-lit areas are less likely 

to have trespassers that could potentially cause harm to the 

bridge. It is important that the street light does not cause 

the area to be over lit, which could cause light pollution and 

take away from the aesthetic value of the surrounding area.

Enclosure Selection

Depending on the functionality of the security system, varying amounts and types of equipment that because of their 

design, construction, and cost will need to be housed in a 

secure location that will also protect them from weather. 

Several methods can achieve this, and much like the selection of all the other aforementioned components, several 

factors should be considered in the selection of the 

appropriate enclosure.

Types of Enclosures

Standard Box—A metal box will prove to be efficient for 

many bridge sites, as many pieces of electrical equipment 

require small components for power and storage of data. If 

cameras are used as part of the integrated security system on 

the bridge site, a small box could easily fit on the pole itself 

where all the cameras are located. If a pole is not available, 

a box may be positioned on some sort of pedestal to allow 

the box to be safely lifted off the ground as to deter any water, insects, or animals from attempting to enter the box.

NEMA Enclosures: It is generally suggested that all enclosures meet a certain standard set by National Electrical 

Manufacturer’s Association (NEMA), and for most applications with these systems the owner should require at 

least a NEMA 4, 4X, 6, 6P. The technical explanations of 

the exact NEMA standards are as follows:

•	 Type 4—Computer enclosures constructed for either indoor or outdoor use to provide a degree of 

protection to personnel against incidental contact 

with the enclosed equipment; to provide a degree 

of protection against falling dirt, rain, sleet, snow, 

windblown dust, splashing water, and hose-directed 

water; and that will be undamaged by the external 

formation of ice on the enclosure.

•	 Type 4X—Protection unit constructed for either 

indoor or outdoor use to provide a degree of protection to personnel against incidental contact with 

the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water, hose-directed water, 

and corrosion; and that will be undamaged by the 

external formation of ice on the enclosure.
Covered Bridge Security Manual

15

•	 Type 6PC—Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with 

the enclosed equipment; to provide a degree of 

protection against falling dirt; to protect against 

hose-directed water and the entry of water during occasional temporary submersion at a limited 

depth; and that will be undamaged by the external 

formation of ice on the enclosure.

•	 Type 6P—Cabinet constructed for either indoor 

or outdoor use to provide a degree of protection to 

personnel against incidental contact with the enclosed equipment; to provide a degree of protection 

against falling dirt; to protect against hose-directed 

water and the entry of water during prolonged 

submersion at a limited depth; and that will be 

undamaged by the external formation of ice on the 

enclosure.

•	 For most scenarios, a NEMA 4 enclosure will protect the electrical components against the elements 

as submersion under water will not applicable 

to most bridge sites and the added cost of higher 

levels of protection will not be required nor warranted. If water coming from multiple directions is 

a problem for a bridge, then a NEMA 4X enclosure 

should be considered

Structure—Some bridge locations will already have a small 

mechanical shed or other enclosed structure on site. This 

could prove to be advantageous for the security system designer for its ability to house the mechanical equipment that 

is required for running a security system. Depending on the 

size and scope of the security system to be installed, it may 

or may not be economically viable to construct a new structure on the bridge site to house the mechanical equipment 

when compared with a box that could be attached to a pole 

or pedestal as mentioned earlier.

Aesthetics: The selection of the enclosure to house all of 

the electrical components of the security system is comparable to the selection of the pole. The box must not have 

a large aesthetic impact on the surrounding area but must 

maintain functionality. Most box set ups that are available 

to the owner will be constructed of metal and will have 

a grey or metal color to them. It is possible, and in many 

applications preferred, to paint the box to match the surrounding area.

Functionality: Once the design team has decided upon 

the exact NEMA type of enclosure that will be used for 

the project, it is important to decide on the exact dimensions of the box. This can be accomplished by taking all 

the equipment that will be placed inside the box such as 

modems, computers, power strips, and any other sensitive equipment that needs to be secured in a weather-tight 

enclosure. Once the team has a list of all the equipment 

that needs to fit into the box, it is important to draw a 

schematic of how everything will fit. Once a rough layout 

is available, take into consideration how many outlets will 

be needed to power all the equipment and exactly what 

type of power strip will be used. Once all this information is available, the team will have a rough idea of the 

size of the box. It is important to order a box that is larger 

than exactly what is needed for minor equipment changes, 

cords, and future expansion.

It is important to understand that the heat that will be generated from the electrical devices within the box will be 

exaggerated by the temperature outside of the box in summer. The temperature within the box can easily become 

hot enough to overheat the electrical components and 

shut off the entire security system. Purchasing a box that 

has a fan or louvers to allow air circulation will add cost 

to the project but will allow the security system to operate through even the hottest months. After-market fans 

and louvers are available to install on boxes that do not 

have adequate ventilation. It is essential that any openings 

in the box protect the components inside from water or 

insects entering and potentially destroying the electrical 

components.

Power Considerations

The remote locations of many covered bridges within the 

United States often make it difficult or expensive to gain 

access to electricity to power the security system. The distance between the closest grid power and the location of 

the bridge may sometimes be so great that running a power 

line to the bridge is not cost effective. If grid power is not 

an economical option, different types and combinations of 

renewable energy sources may meet the needs of the system. 

Renewable energy will be discussed in full detail later on 

this section of the report.

Grid Power

If a hook up to grid power is readily available and economically viable, it will typically be the best choice as it will be 

the most dependable source of electricity. It is important to 

have a constant source of power with any security system to 

ensure that it works with the least amount of down time. The 

only problem with grid power is the reoccurring cost from 

the local electric company for using their services. Given 

that the draw from a typical security system is relatively 

small, the charges will also generally be minimal.

Renewable Energy

It is prudent to consider using multiple sources of renewable 

energy when setting up this type of system because any one 

source will not be consistent at different periods of time. 

Wind power only works when a substantial wind is occurring and solar power will only generate electricity during 

daylight hours, with energy output varying with the intensity 

of the sunlight. By using both systems, you will increase the 
General Technical Report FPL–GTR–223

16

chances that one of the sources will be generating enough 

electricity for the security system. For times when not 

enough power is being generated, batteries must be used to 

store electricity if grid power is not available. It is possible, 

however, that one source of power will suffice if the draw 

from an individual security system is relatively small and 

the battery bank is relatively large and can provide adequate 

reserve power.

Using renewable energy to power a security system is a 

large undertaking and should be thoroughly considered before and during design. Compared with a direct city link for 

electricity, a renewable energy system will require notably 

more planning, maintenance, up-front cost, and patience. 

This fee will not occur with the use of renewable energy 

sources, but a city hook-up will not have the large up-front 

cost associated with setting up a renewable energy system.

Some systems may elect to use both grid power and a renewable energy system. A system of this type will use renewable energy whenever it is generated and use the grid as 

a backup if the renewable energy sources stop producing energy. By using this type of system, you can also use energy 

that is generated and stored. Some electric companies will 

allow you to generate electricity for them and will pay you 

incentives to do so. These incentives have the possibility of 

paying back the fee associated with using the grid power 

and possibly even pay for the security system itself.

Multiple types of renewable energy systems currently exist and several other sources are on the horizon. Although 

multiple sources of alternative energy exist, only a few will 

be useful at most covered bridges sites given their isolated 

locations and natural surroundings. The only sources of 

alternative energy that will discussed within this report are 

wind and solar power, as these are the two sources that will 

likely be present at most covered bridge sites.

Wind—Blades of a wind turbine harness energy from the 

wind and turn it into electricity through the movement of 

the blades. Ideally, a wind turbine should be placed in an 

area that has constant, nonturbulent wind. We recommend 

that the wind turbine be placed at least 30 ft above the 

ground and 300 ft away from all obstructions that could 

cause turbulent wind (e.g., structures, trees, changes in terrain). These distances are only recommendations and may 

be shortened, but optimal performance of your wind energy 

system will be at distances that equal or exceed these recommendations. Different companies may have different recommendations for placement of their particular wind turbines, 

and it is important to follow them as closely as possible to 

get the maximum efficiency from the equipment.

In general, the more power required from a wind turbine, 

the greater the blade diameter required. The blade diameter 

often becomes a limiting factor when designing a hybrid 

energy source depending on what is allowed by city ordinances and historic structure limitations. It is important to 

realize that the wind turbine will be placed within close 

proximity to a covered bridge that is a draw for tourism and 

the local economy, so care must be taken to not detract from 

the aesthetics of the surrounding area.

When sizing the wind turbine for a particular security system, it is important to realize that the rated output for the 

turbine is for the optimum wind speed, which will not be 

the average wind speed in many instances. These speeds can 

meet or exceed 20 to 30 miles per hour with most types of 

wind turbines, which is not a constant wind speed in most 

areas. It is important to review and consider the wind speedto-power output graph that is supplied with most turbines to 

choose the correct equipment that will produce the proper 

power output at average wind speeds at the bridge site. 

Figure 6 shows a wind speed to power output graph for a 

600-watt wind turbine and shows that it will only produce 

600 watts of power if the wind speed meets or exceeds 

26.4 mph. This power curve has been measured under laminar wind conditions with the load connected directly to the 

generator.

For security systems with “lower” power requirements, 

100 to 10,000 watts, there are two main types of wind turbines that should be able to produce the needed power: the 

horizontal axis wind turbine and the vertical axis wind turbine. Each type of wind turbine has its distinct advantages 

and disadvantages and there must be a benefit/cost analysis 

done to consider price, efficiency, and power output for the 

type of power output needed for a particular security system. The vertical axis turbines are well suited for smaller 

applications such as a security system and can survive wind 

gusts better than most horizontal wind turbines. It is important to discuss with the manufacturer the exact requirements 

needed for the security system and the environment where it 

will be installed.

Figure 6. Wind speed to power output graph for 600-watt 

wind turbine. Source: Urban Green Energy 600-watt wind 

turbine specifications. Urban Green Energy Inc., New York. 
Covered Bridge Security Manual

17

Solar—Solar panels harness the sun’s energy and efficiently 

convert it to electricity. Solar panels continue to become 

more efficient as the technology improves, making them 

smaller and more efficient; that said, size is still a main factor in the selection of a solar power system. Current technology allows 10 watts per square foot of solar panel according to top solar companies available for distribution in the 

United States (Anon 2011). Some panels will give you more 

or less wattage per square foot depending on price and the 

advancements in technology within the company. It is important to realize that an increase in efficiency will generally 

relate to an increase in price.

Although solar power can be an efficient source of renewable energy, it should not be thought of being without 

limitations. Because most security systems will need to be 

functional at all hours of the day, it is essential that a constant source of power is available day and night. Therefore, 

because solar power is only available during the day, it is 

essential to incorporate an adequately sized battery bank and 

potentially couple it with wind power or grid power to allow 

for uninterrupted power day and night.

Battery Bank—Batteries are important for any renewable 

power source system for moments when not enough sun or 

wind can generate the power needed to run the monitoring 

equipment. To design the proper battery bank for your system, it is important to know the power draw of your security 

system at peak performance, average hours of sunlight in 

your area, and the average wind speed in your area. Most renewable energy companies will be able to help you estimate 

the natural conditions at the bridge site depending on which 

part of the country the bridge is located. There are also multiple resources online with this information.

Batteries are designed specifically for renewable energy 

sources, but marine or deep cycle batteries are also quite effective if designed and sized properly. Because the system 

will create a steady draw from the batteries even though the 

batteries will not get a consistent charge, it must ensure that 

the batteries will not fall below 50% of their amp hour capacity so no damage occurs to the batteries. Once batteries 

have fallen below a certain percentage of their amp hours, 

they may not be able to become fully charged with the aid of 

a renewable energy system.

Inverter—The inverter converts the DC power created by 

the renewable energy sources into usable AC power. Two 

main types of inverters can be used for this application: the 

pure sine wave and a modified sine wave. A modified sine 

wave inverter is less expensive but does not produce the 

type of power required by sensitive equipment. Pure sine 

wave inverters are more expensive but are the appropriate 

choice for this application. Much like the solar panels and 

wind turbines, the inverter is not 100% efficient, so it will 

be required to increase the power supply to compensate 

for this loss across the inverter. It is important to research 

different companies that produce pure sine wave inverters 

and purchase one that meets or exceeds the requirements 

for the particular security system.

Controller—A renewable energy source will continue to 

charge the batteries indiscriminately if left unattended, 

which may overcharge the batteries and potentially damage 

them. Therefore, a charge controller is necessary to monitor 

the level of charge of the battery bank and manipulate the 

level of charge to the battery as needed. There are as many 

types of controllers as there are renewable power sources, 

so it is essential that a manufacturer’s specification meet or 

exceed the requirements of the power system installed.

Set-Up

Several important steps are associated with set-up of the 

security system to ensure that it is aesthetically pleasing and 

functional. Although many of the major pieces of equipment 

have been discussed in great detail in previous chapters, it 

is important to have an understanding of all auxiliary equipment and components that are required to make the entire 

system functional. These materials include the type of conduit, wires, encasements, and the equipment to attach the 

box to the poll. More equipment may be required for a particular security system, depending on the location and type 

of system that will installed.

Conduit

To prolong the life of all wires and equipment, it is important to use conduit to run wires whenever possible. Several 

types of conduit could be used, including PVC, metal, or 

plastic. The design team should run an economic analysis 

deciding how vulnerable the wires are underground and how 

much each type of available conduit costs. It is important 

to choose a safe option that will adequately protect all the 

equipment, but it isn’t necessary to always choose the strongest alternative. All conduit should meet or exceed all fire 

and electrical codes in the area of installation. The conduit 

should also be strong enough to protect against animals or 

insects penetrating the conduit and destroying the wiring.

Wiring

Wires come in a variety of sizes and types that range in price 

and functionality. These two main properties of wire are two 

of the biggest decisions when deciding on what type of wire 

should be used for any particular piece of equipment. Some 

equipment will have a minimum requirement for wire size 

to reduce resistance and improve the functionality of the 

piece of equipment itself. Table 2 demonstrates that as the 

gauge number of wire decreases, the diameter increases and 

the resistance decreases. A decrease in wire gauge will also 

lead to an increase in price per length, so it is not always 

practical to use the smallest gauge wire to increase functionality unless it is economically viable. If there is considerable 

distance between the equipment and from the power source, 
General Technical Report FPL–GTR–223

18

then a decrease in wire size may be required to reach an 

acceptable level of functionality.

Conduit can be easily used for running wire for certain applications such as underground or up a pole, but it may be 

difficult to use conduit within the bridge structure itself. All 

wire that is run without conduit should have a covering that 

can ensure proper protection. Within the bridge itself may 

be the possible threat of insects and small animals such as 

rats, birds, and squirrels; it is essential that all wiring be 

adequately covered to ensure that the wildlife will not be 

able to penetrate the coverings.

Attachment Devices

All equipment must be attached to either the bridge or other 

surrounding structures including poles or other structures. 

It is essential that all equipment is attached as securely as 

possible with a minimum of disturbance; this is especially 

true within the bridge structure itself. Many covered bridges 

have existed for over 100 years and it is critical that the 

security system being installed does not change the original 

design or construction of the covered bridge to preserve 

the historic significance of the bridge. If large alterations 

are completed on the bridge, it is possible that the bridge 

may not be eligible to be placed on the Register of Historic 

Places as mentioned earlier on in this report. Whenever 

screws or other attachment devices penetrate into the existing bridge, it is important to use the smallest size possible to 

minimize the permanent damage to the bridge.

Encasements

When ordering the equipment for a particular security system, it is important to notice the ability of the equipment 

to handle an outdoor atmosphere. Some types of equipment will be designated for indoor-only applications unless 

certain guidelines are met, such as the use of watertight 

enclosures. This is an often overlooked part of the security 

system but is important to the longevity of the system. Some 

proprietary systems will have casements for their products 

to protect them from exterior exposure while others may 

require the use of another system.

Some encasements may also be used in certain applications to increase aesthetic value of the equipment. These 

types of encasements may appear in the form as a wooden 

box around the equipment to give the appearance of a bird 

house, as seen in Figure 7. By using the same wood as the 

surrounding bridge, the flame detector shown in Figure 8 is 

not as aesthetically distracting as it is without the use of an 

encasement system. The simple act of painting the existing 

encasement of equipment to match its surroundings can be 

beneficial and will not detract from its aesthetic effect.

Supplementary Equipment

For any security system involving electronic components, 

it will be required to have supplementary equipment so that 

all components can operate efficiently. As mentioned earlier, 

it is important that someone knowledgeable about security 

systems, such as an IT professional, assists in the installation of all electronic equipment. Most electronic equipment 

will have software that may require manipulation to have 

the most efficient settings possible.

Communication Devices

It will be desirable for some information recorded at the 

bridge sites to be sent to a remote destination through the 

Table 2. American Wire Gauge (AWG) 

chart for diameter, area, and resistance 

AWG 

Diameter 

(mm) 

Cross

sectional area 

(mm2

)

a

Resistance 

(ohm/m) 

0000 11.7 107.0 0.000161 

000 10.4 85.0 0.000203 

00 9.26 67.4 0.000256 

0 8.25 53.5 0.000323 

1 7.35 42.2 0.000407 

2 6.54 33.6 0.000513 

3 5.83 26.7 0.000647 

4 5.19 21.2 0.000815 

5 4.62 16.8 0.00103 

6 4.11 13.3 0.00130 

7 3.67 10.6 0.00163 

8 3.26 8.35 0.00206 

9 2.91 6.62 0.00260 

10 2.59 5.27 0.00328 

11 2.30 4.15 0.00413 

12 2.05 3.31 0.00521 

13 1.83 2.63 0.00657 

14 1.63 2.08 0.00829 

15 1.45 1.65 0.0104 

16 1.29 1.31 0.0132 

17 1.15 1.04 0.0166 

18 1.02 0.82 0.0210 

19 0.91 0.6530 0.0264 

20 0.81 0.5190 0.0333 

21 0.72 0.4120 0.0420 

22 0.64 0.3250 0.0530 

23 0.57 0.2590 0.0668 

24 0.51 0.2050 0.0842 

25 0.45 0.1630 0.106 

26 0.40 0.1280 0.134 

27 0.36 0.1020 0.169 

28 0.32 0.0804 0.213 

29 0.29 0.0646 0.268 

30 0.25 0.0503 0.339 

31 0.23 0.0415 0.427 

32 0.20 0.0314 0.538 

33 0.18 0.0254 0.679 

34 0.16 0.0201 0.856 

35 0.14 0.0154 1.08 

36 0.13 0.0133 1.36 

37 0.11 0.0095 1.72 

38 0.10 0.0078 2.16 

39 0.09 0.0064 2.73 

40 0.08 0.0050 3.44 

a

 Resistance of copper at 20 °C. 
Covered Bridge Security Manual

19

Storage Devices

It will be important that some data are stored at the bridge 

site if not all information is sent to a remote location. 

Depending on the abilities of the communication devices 

selected, it may not be possible to send all information required through wireless sources. A storage device can be as 

simple as a desktop computer or can be much more complex 

with secure electronic storage cabinets that can be found 

through multiple manufacturers. It will not be cost-effective 

in most applications to store all information that is recorded 

at the bridge site but to only record certain information. This 

can include certain time periods after an alarm has been set 

off or during certain times of the day.

Software

Numerous software options are available for designing a 

monitoring system on a covered bridge. Some of these software options may be proprietary depending on the piece of 

monitoring equipment that is selected by the design team. 

For the system to be as effective as possible, it is essential 

that the correct software is chosen and the correct settings 

are selected within the software. In-depth software analysis 

is not discussed in further detail within this report because 

of the numerous options available. It is important to work 

with the manufacturer of the monitoring equipment to allow for optimum efficiency from all equipment within the 

system.

Testing

Testing is one of the most important aspects of creating an 

effective security system. All components should be able to 

fulfill or exceed their individual assignments, and the security system as a whole should be able to achieve a high level 

of security for the bridge as a whole. It should be stated that 

all fire testing, both in the lab and especially in the field, 

should be conducted in the safest possible fashion to ensure 

that there is no damage to any personnel, equipment, or 

property.

In-House Testing

It is crucial that all individual components of the security 

system are tested in-house before they are installed and tested at the bridge site. It is easier to troubleshoot equipment 

that is not working properly in an easily accessible, controlled atmosphere as compared with the bridge site, which 

may have inclement weather and equipment in hard-to-reach 

areas. Not only should the individual components be tested 

individually but the entire systems should be tested together 

to ensure that all parts of the system work together to reach 

the end goal of adequate protection of the bridge site.

In-Field Testing

As mentioned before, testing in the field should be conducted in the safest possible fashion. Before creating an 

Figure 7. Flame detector in covered bridge without encasement (top) and with encasement (bottom).

Figure 8. Cameras, antenna, and enclosure schematic at 

bridge site.

use of communication devices. The information recorded by 

the monitoring systems will prove to be useless if they cannot be seen by others at remote locations such as local fire 

departments or police stations. There are multiple ways of 

transferring this information to outside sources, but for more 

bridge sites, the use of directional antennas to access wireless connections will be the best option. Directional 

antennas allow for optimum signal in areas where cellular 

coverage may be low, which is typical in some isolated 

covered bridge locations.
General Technical Report FPL–GTR–223

20

open flame around, on, or within the covered bridge itself, it 

is essential that all proper officials are notified to avoid any 

problems with passersby from reporting the testing crew. 

Once all officials have been notified that fires will be started 

on the bridge site, it is essential that safety precautions such 

as fire extinguishers and buckets of water are on hand and 

close by in case a fire gets out of control.

Different equipment will have different thresholds at which 

they will be set off and trip an alarm. A typical fire for a 

flame detector may be a 1-ft by 1-ft2 fire from a distance 

of 60 to 70 ft. This can easily be simulated by placing an 

adequately sized fire proof pan on a cart so it can be pushed 

around the bridge to ensure that all areas of the bridge are 

secure. This is essential to ensure that all cameras and detectors are pointing in the most efficient direction, and any adjustments can be made before the system is considered fully 

operational.

Infrared or other types of cameras may be motion detectors 

or be set to a certain temperature threshold. These should 

be tested at night when they would normally be operational 

and monitoring the bridge site. A fire may be started at one 

of the openings or inside the bridge within the line of sight 

of the cameras to ensure that the entrances of the bridges are 

secure from trespassers.

Summary

Covered bridges are an important part of history of the 

United States and must be maintained for future generations. Unfortunately, these bridges are being destroyed at 

an alarming rate from arson, vandalism, and neglect. It is 

essential that covered bridge owners know the importance 

of maintaining the structural and aesthetic integrity of their 

bridges. As stated earlier in this report, The FHWA Blue 

Ribbon Panel Workshop on Bridge Security Assessments

has decided on five different levels of security to construct 

an effective defense against unwanted activities. These 

levels of security include deter, deny, detect, defend, and 

strengthen structures. The five parts of the security plan 

proposed by the BRP are equally important if implemented 

correctly. This report has taken an in-depth look at the different security and monitoring equipment that can be used at 

covered bridge sites.

What These Levels of Bridge Security Hope 

to Accomplish

Bridge owners that implement the levels of security discussed in this report should not expect their bridges to be 

indestructible but must realize that this increased level for 

security will greatly improve the chances that the bridge will 

survive for generations to come. It is impossible to make a 

structure perfectly secure but it is the responsibility of the 

bridge owners to make the structure as secure as possible 

within the economic and aesthetic limits of the bridge site 

and the financial situation of the bridge owner. As 

mentioned numerous times throughout this report, it is 

essential that all levels of bridge security are covered.

Maintenance

The implementation of these security and monitoring devices should not be considered the end of any security 

project. Constant monitoring of all equipment and periodic 

maintenance of both the equipment and the bridge itself are 

vital to the survival of the system and the bridge. It may be 

required to renovate the bridge both aesthetically and structurally throughout its life and both of these issues are discussed briefly in the recommendations portion of this report 

and also in great detail in Covered Bridge Manual by Phillip 

Pierce. Within years or even months, a monitoring or security system can prove to be obsolete and may not be able to 

fulfill its initial requirements.

Recommendations

Protection against arson and vandalism alone will not ensure 

the safety and longevity of the Nation’s covered bridges. 

Other preventative measures must be taken as often as 

possible so the bridges do not succumb to other natural or 

manmade disasters. There is extensive coverage on the types 

of preventative measures that should be taken with historic 

covered bridges in the Federal Highway Administration 

Covered Bridge Manual published in April 2005 in 

Chapter 17, “Preserving Existing Covered Bridges.” Topics 

included in this report are controlling water runoff, roof and 

siding protection, foundation support, regular cleaning, and 

fire protection. The FHWA report goes into other preventative measures for covered bridges (Pierce and others 2005).

When an extensive search for security and monitoring 

systems on covered bridges through the United States was 

conducted, we found that the most-used type of protection 

for covered bridges was the use of flame-resistant materials. 

These types of products tend to have a low cost for how effective they can be and may only need maintenance every 

5 to 10 years. Most covered bridge owners may not have 

large sources of funding and a large scale monitoring system 

may not be financially reasonable. Bridge owners may also 

have difficulty with the heavy amount of maintenance that 

may be required for some monitoring or security systems.

Education

Physical protection is not always enough when it comes 

to the preservation of our national historic landmarks. 

Education can be an important tool when it comes to preservation. Integrating covered bridges into the school system 

can teach the importance of these structures to younger students both in areas that have covered bridges and areas that 

do not. These educational benefits should include knowing 

from what era these bridges came, why they were built the 

way they were, and why they should stand for as long as 

possible as monuments of past. Not only should the benefits 

and historical significance of these bridges be discussed in 
Covered Bridge Security Manual

21

an educational setting, but the legal ramifications of damaging these bridges must also be addressed. Many people 

may not fully understand that most of these covered bridges 

are Federally protected, and damaging them can come with 

large fines and even jail time depending on the severity of 

the crime committed against them.

Phases of Monitoring or Security System

Four important phases of deploying any monitoring or security system must be thoroughly discussed before any portion 

of the project begins. For larger bridge owners, such as state 

DOTs or local governments, it may be possible for all portions of the monitoring or security system to be completed 

in house but this may not be possible for smaller bridge 

owners that do not have the capacity. To avoid any problems 

with the system and ensure that the system is as effective as 

possible, it is essential that all parties involved are aware of 

all arrangements and expectations.

Design

The design of the monitoring or security system can be very 

challenging and time consuming, depending on the level 

of security desired and the complexity of the system. If an 

intricate monitoring system is chosen, then software and 

hardware will be required and this in itself can become a 

very expensive and challenging problem. For small bridge 

owners who do not have the capacity of resources for this 

level of design, then it may be appropriate to outsource the 

design of the system.

Installation

Installation of any security or monitoring system heavily depends on the complexity and scope of the system. If the system is not very technical, then the installation could be completed by someone outside the security profession. If there 

are multiple pieces of equipment that must work in unison, 

then it may be in the best interest of the bridge owner to 

have a third party install all the equipment. In many cases, 

the company or individual that designs the system may be 

the same one that installs the system to guarantee that it is 

done correctly.

Monitoring

It does not matter how well any system is designed or installed if there is no one to monitor it and respond to any 

alarms. In most monitoring applications, the system must be 

monitored by a designated person who is able to react to any 

type of arson or vandalism. It is important to know what the 

procedure will be if any alarm is set off at the bridge site. If 

there are cameras at the bridge site, it may be possible to remotely view the bridge site after any alarm has been set off 

to see if it is a false-positive alarm.

Maintenance

The implementation of these security and monitoring devices should not be considered the end of any security project. 

Periodic maintenance of both the equipment and the bridge 

itself are vital to the survival of the system and the bridge. It 

may be necessary to renovate the bridge both aesthetically 

and structurally throughout its life, and both of these issues 

are discussed briefly in the recommendations portion of this 

report and also in great detail in Covered Bridge Manual

(Pierce and others 2005).

Madison County Project

The authors of this report have taken part in a security effort 

with Madison County in southwest central Iowa to protect 

five of the six covered bridges in the county. The bridges included within this effort are the Cutler–Donahoe, Hogback, 

Holliwell, Imes, and Roseman. The Cedar Bridge had a similar security system installed in 2005 by a team consisting of 

many of the same members. The Cedar Bridge project will 

be discussed in some detail with a full report on the entire 

project also available.

History of the Covered Bridges of 

Madison County

At one point, there were 19 covered bridges in Madison 

County but because of various reasons, all but five have 

been destroyed. Although it is unfortunately common for 

covered bridges to slowly disappear over the years, there 

has been a push in recent years to protect these historic 

landmarks. The bridges of Madison County have received 

heightened awareness because of their increased fame in 

part from the book, The Bridges of Madison County. This 

book, written in 1992 by Robert James Walker, was quickly 

turned into a major motion picture by the same name in 

1995 starring Clint Eastwood and Meryl Streep (Walker 

1992). In 1993, the book received more attention by being 

named “the book of the year” by Oprah Winfrey, which 

raised the status of the book and bridges to even a higher 

level.

Unfortunately, this fame did not protect the six remaining 

bridges at the time. The Cedar Bridge, the main bridge in 

The Bridges of Madison County, was completely destroyed 

in 2002 along with a house that was a major landmark in the 

book. The Hogback Bridge, which also appears in the book, 

was set on fire in 2003 but the fire was quickly extinguished 

by local passersby. The Cedar Bridge was completely rebuilt in 2003–2004 and the Hogback Bridge was completely 

renovated from its damages. These appalling actions caused 

the County of Madison to team with Iowa State University’s 

Bridge Engineering Center and the USDA Forest Products 

Laboratory to install security measures on the Cedar Bridge 

to dissuade any further damage to the structure.

Because of the effectiveness of this project in 2005, it was 

decided in 2010 that surveillance equipment of a slightly 

different variety should be implemented on the other five 

bridges. The remainder of this case study deals exclusively 

with the project in 2010–2011 and the five bridges included.
General Technical Report FPL–GTR–223

22

Security Equipment Installed

The same security system was installed on all five bridges 

included in the 2010–2011 project. The system included a 

total of two cameras and two detectors: an infrared camera, 

an optical camera, and two flame detectors per bridge. In 

addition to the security equipment, numerous communication devices were installed within an enclosure that allowed 

for storage or information and remote connection to the 

surveillance equipment via cellular internet connection. The 

only major difference between systems was at the Hogback 

Bridge where alternative energy sources were used to power 

the surveillance system. This alternative energy system is 

discussed in detail in the Hogback Bridge section of this 

report.

When compared with the Cedar Bridge Security System installed in 2005, the main difference is that the Cedar Bridge 

was outfitted with fiber optic temperature sensors. Because 

of the problems faced by the design team during installation and testing of the fiber optic cables, we decided to not 

use fiber optic technology on the Cedar Bridge. Fiber optic 

cables can prove to be an effective means to protect a covered bridge but multiple problems can arise if not installed 

and operated correctly, as discussed earlier in the equipment 

portion of this report.

All equipment in the security system for this project was 

chosen by an information technology professional with 

experience within the field of security systems. Advanced 

software settings are not discussed in this report, as they 

are extensive. Also, information involved in programming 

all equipment to work properly within the system and all 

proprietary systems will have differing system set-ups. It 

is important to carefully read all instruction manuals and 

ensure that all proper settings are chosen while designing a 

surveillance system so that the optimum capabilities of the 

system can be obtained.

The overall system monitoring is completed with a local PC 

running custom-developed software with communications to 

all devices being made via a local area network with wireless and wired communication capabilities. Communications 

outside of the local area network are handled by wireless 

cellular radio. Three subsystems are used by the monitoring system: a Web camera, an IR camera, and UV/IR flame 

detectors. From the IR camera technology, the system will 

monitor output from the camera and detect a predetermined 

maximum range in which a heat signature will cause the 

system to activate the alert status. The UV/IR flame detector system uses signal conditioners that convert voltage into 

readable digital values. When the flame detector detects the 

presence of a flame, it completes an electoral circuit. The 

voltage from this circuit is read by the monitoring system 

and if it falls within the positive voltage range expected, an 

alert status will be activated.

When an alert status is activated, the monitoring system 

software activates the optical and infrared cameras to begin 

collecting buffered imagery from the camera for a specified time frame. For this project, it was decided to record 

the optical camera for roughly a minute and a half and the 

infrared camera for roughly 3 minutes. Unfortunately, this 

recorded video was not able to be sent wirelessly and has to 

be retrieved manually by the design team. Also, during this 

time, an email message is generated and sent by the wireless 

cellular radio network connection to identified recipients 

indicating an alert status has been reached

Both active and historical images are viewable by anyone 

who has the system passwords. This was made possible with 

a cellular modem and a high-gain antenna.

Communication Devices

As mentioned in the previous section, multiple devices 

used on this project were for communication purposes so 

personnel could remotely access the surveillance system 

by an internet connection or to enhance the performance of 

the surveillance equipment. These items include a wireless 

router, personnel computer, cellular modem, Web-based 

remote power switch, signal conditioners, micro servers, 

power supplies, and power injectors. There are many proprietary systems available for these types of communication 

devices and the following list of equipment choices are only 

the selections made the by the BEC design team based on 

previous projects with similar applications. It is important 

for any individual design team to choose equipment that can 

be integrated. The team must feel comfortable using and 

configuring the equipment.

Wireless Router—An 11G Wireless Nano Router (ESR1221 EXT) was used to extend a wireless signal to the 

equipment being used on the bridge. This specific type of 

router has an upgradeable antenna for an increased wi-fi 

coverage area.

Personal Computer—The personal computer used on this 

project monitored the entire system in real time. It was also 

used to store images that are taken by all cameras during the 

case of an alarm being set off.

Cellular Radio—In addition to a directional antenna, we 

used a wireless cellular broadband modem so that all 

information can be accessed from remote locations.

Web-Based Remote Power Switch—A specific type of remote power switch has a timer function allowing a reboot or 

shut down times without any actions by in-field personnel. 

This power switch and its software was used to allow personnel to remotely control four power outlets at one time.

Power Injector for Optical Camera—The power injector 

used for this project was the POE – IPX-INJ-C. The injector 

delivers both data and electrical power to ethernet-enabled 
Covered Bridge Security Manual

23

devices using a single ethernet cable. This eliminates the 

need to place the ethernet-enabled device, such as the optical camera, near an outlet and gives more freedom to the 

security system designer on the placement of the device.

Equipment for Flame Detector—The following equipment 

was used exclusively for the flame detectors.

Signal Conditioners—Two signal conditioners are used 

for every flame detector at all bridge sites to reduce false 

positives.

Microserver—A microserver was used on this project to 

connect the signal conditioners to the wireless connection.

Power Supply—A power supply was used to power both 

of the flame detectors, and another was used to power the 

relays in both of the flame detectors.

Cameras and Detectors

As mentioned earlier in this section, each bridge site has 

a total of two cameras and two detectors including an infrared camera, an optical camera, and two flame detectors. 

Figure 8 shows the placement of each piece of equipment 

that is outside of the box. The antenna, IR camera, optical 

camera, and enclosure are located on the pole roughly 

100 to 150 feet away from the bridge, whereas the flame 

detectors are located within the bridge itself. The exact 

placement for each bridge site is seen later in the section 

when each bridge is discussed individually.

Flame Detector—Two flame detectors were installed on 

each of the five bridges in Madison County on either end of 

the bridge positioned to cover the largest portion of the interior of the bridge as possible. There were multiple problems 

when installing these flame detectors including cross bracing and other structural members interfering with the most 

ideal line of sight. The final placement of the flame detectors 

for each bridge is shown later.

The flame detector selected for this project senses radiant 

energy in the ultraviolet (UV), visible, and wide band infrared (IR) spectrums within a 120° of vision. The settings 

for the flame detectors were set at the 50- to 60-ft range, 

as most of the bridges are roughly 100 to 120 ft long from 

opening to opening.

To transfer the signal from the flame detectors to the data 

collection hardware where its conditioners were located, a 

trench was dug from the equipment pole to an entry point on 

the bridge. For most of the bridges, it was easiest to trench 

to the wooden approach span between the abutment and the 

bridge opening. From the underside of the approach span, 

the wire could be easily routed through the bridge to the 

flame detectors without being seen from the bridge deck. 

The Cutler–Donahoe Bridge had a newly paved road between the pole and the bridge, so directional boring had to 

be used in order to not disturb the road. The directional bore 

had minimal disturbance except for the entrance and exit 

points near the pole and the bridge and would be an option 

for bridge locations where open trenching is unwarranted or 

undesired.

The flame detectors might not be aesthetically pleasing and 

would contrast with the rest of the bridge; therefore, we 

decided to cover the flame detectors with a wooden case 

that would take on the appearance of a bird house and be 

relatively unnoticeable when compared with the white metal 

case. Each camera was also painted brown so as to not draw 

attention to it when seen through the hole in the box. The 

flame detector with and without the wooden case can be 

seen in Figure 8. 

Infrared Camera—For this project, only one infrared (IR) 

camera per bridge was positioned at a certain distance from 

one bridge entrance, usually within 50 to150 ft to the nearest 

bridge entrance. The infrared camera used on all five bridges 

has the ability to produce thermal images in real time at a 

resolution of 384 by 288 pixels. An enclosure provided by 

the manufacturer was used to protect the camera from the 

elements and individuals who would want to damage the 

camera with projectiles or through other measures. The enclosure for the IR camera had a glass lens that was coated in 

germanium for optimum thermal transmissivity.

Figures 9 and 10 show images that the IR camera produces. 

Each image shows the capture date and time as well as the 

spectrum of temperatures within its field of view, including high and low temperatures. For each of these bridges 

a person stands within the opening of the bridge. The IR 

camera points out this area of increased temperature when 

compared with the surroundings with an arrow and a box 

with the temperature in it. If these maximum temperatures 

reach a certain threshhold, then then the IR camera can set 

off an alarm.

Figure 9. Infrared camera image at Cutler–Donahoe 

Bridge.
General Technical Report FPL–GTR–223

24

Optical Camera—Directly next to the infrared camera was 

an optical camera. The optical camera provided a similar 

service as the infrared camera except, instead of providing 

images in the infrared range, they provided images in the 

visual spectrum. These images were also transmitted in real 

time over the internet. The camera chosen for this project 

is designed for outdoor use so no enclosure was required 

before installation. This camera has the ability to pan and tilt 

through remote controls that could be controlled remotely.

Figures 11 and 12 show the image that the Panasonic optical 

camera produces. Compared with the IR camera, this image 

is fairly basic and is used for simple surveillance purposes. 

When an alarm is set through the IR camera of flame detector, the optical camera will record video for a specified 

amount of time and store it for future viewing so personnel 

can see what caused the alarm to trigger and to have video 

evidence of any individuals who may be on the bridge during times when the bridge is closed.

Other Equipment—Box

The equipment box storage used at each bridge was the 

same. A NEMA 4 box, which is the desired classification 

of box to be used for most applications as stated earlier 

in this report, which measures 24 in. by 24 in. by 8 in. 

(H × W × D), was used to store the monitoring equipment 

at the bridge. A rough sketch (Fig. 13) showed considerable 

room for expansion but after placing everything inside the 

box in the field, it proved to have very little extra room with 

the inclusion of all wires and power supply cords. This can 

be seen in Figure 14 with the actual in-field layout of the 

NEMA enclosure.

Because the NEMA enclosure was built to be hung on a flat 

surface, brackets had to be fabricated to secure the boxes 

to the monitoring equipment pole (Fig. 15). These brackets 

were made with basic 1⁄4-in. steel bars that had drilled holes 

for lag screws and bolts. At the four points where the box 

was attached to the brackets, an eye bolt was used so aircraft 

wire could wrap around the pole to provide additional support against the box swaying in the wind.

Challenges with Each Bridge

Cutler–Donahoe

The biggest obstacle with the Cutler–Donahoe Covered 

Bridge was its location. The Cutler–Donahoe has been 

moved from its original location to a city park within the 

downtown area of Winterset, the county seat of Madison 

County. Because it was located within a city park, it was 

more difficult to get close to the bridge to complete any necessary construction or attachment of any cameras. A newly 

constructed road between the ideal pole location and the entrance of the bridge caused multiple problems with trenching for the flame detectors on the bridge as well as getting 

power from the bridge to the pole.

Initially, we thought that for obvious security reasons the 

NEMA enclosures should be installed at a height on the 

poles such that any vandalism or damage would be difficult 

to accomplish. Therefore, for the first bridge instrumented, 

the Holliwell Bridge, the enclosure was installed 

Figure 10. Infrared camera image at Holliwell Bridge.

Figure 11. Optical camera image at Cutler–Donahoe.

Figure 12. Optical camera image at Holliwell.
Covered Bridge Security Manual

25

keep all equipment at a higher level (8 ft or more) to deter 

trespassers.

The flame detectors for the Cutler–Donahoe Bridge 

(Fig. 17) were required to be placed in the middle of the 

openings because of the architecture of the bridge. This 

caused multiple problems because cross members tended to 

get in the way of a direct line of site for the detectors. Other 

bridges allowed side mounting of the flame detectors so that 

cross members and other structural members did not inhibit 

Figure 13. Box layout for NEMA enclosure.

Figure 14. Actual box layout in field.

Figure 15. Brackets for box to pole connection.

approximately 20 ft from the base of the pole. Shortly thereafter, we determined this was not very user friendly, but also 

not necessary if other precautions were made. On the subsequently instrumented bridge, the Cutler–Donahoe Bridge, 

the NEMA enclosure was set roughly 8 ft off the ground as 

seen in Figure 16. We later determined that this height was 

still unnecessary and that setting the enclosures at chest 

height level was sufficient as long as enclosures were properly marked and securely locked. The bridge owner decided 

on the mounting height of all equipment. If the bridge site 

has had problems with vandalism, it may be necessary to 

Figure 16. Cutler–Donahoe pole.
General Technical Report FPL–GTR–223

26

a direct line of a site and were placed optimally. It is essential when installing all equipment, both in the bridge and 

around the bridge site, to balance the aesthetics of the bridge 

site with the functionality of the equipment.

Hogback

The Hogback Covered Bridge proved to be the most difficult bridge out of the five instrumented. Because of the isolation of this particular bridge, it cost as much to install line 

power from the local municipality as it would be to set up 

a renewable energy system that used solar and wind power 

in the area. Neither the BEC nor the County of Madison 

had ever tried to develop such a large, stand-alone alternate 

energy system prior to this project, so there were initial 

uncertainties of such an undertaking. After discussing this, 

we decided to use alternative energy sources with the aid of 

Figure 17. Cutler–Donahoe flame detector that has been 

activated.

Figure 18. Hogback enclosure set up.

renewable energy professionals. As seen in Figures 18 and 

19, three additional NEMA enclosures for the renewable 

energy equipment and a 60-ft pole to house the solar panel 

and wind turbine were required. All of this equipment will 

be discussed in the following section.

Alternative Energy System—Because a solar panel or wind 

generator are only rated for ideal conditions, it was important to size all of the equipment for average conditions with 

a certain safety factor added in case of an extended downtime. After reviewing historical numbers from Madison 

County, we decided to select a 600-watt wind generator and 

a 150-watt solar panel with the use of a battery bank that 

could store reserve power for up to 3 days without stopping 

the security system (Fig. 20).

Wind Turbine—Instead of using a horizontal axis wind 

turbine, which is the more common type of wind generator, 

we decided to use a vertical axis wind turbine that could 

use less wind speed for more power. There is also a lesser 

chance that the vertical axis wind turbine will be damaged 

by sudden wind gusts when compared with its horizontal axis counterpart, which is ideal for the application in 

Madison County. Another difference between this system 

and others of similar size is that a common 60-ft telephone 

pole was used rather than a proprietary pole. Most manufacturers will only warrantee their equipment if it is placed on 

the pole that they also manufacturer, but some manufacturers will allow their systems to be placed on a professionally 

installed telephone pole. Significant savings can be seen by 

not having to purchase a proprietary pole for a wind turbine 

or solar panel. 

Figure 21 shows the construction of the wind turbine within 

a laboratory setting for testing of power output at different 

wind speeds. For a frame of reference, the BEC employee 

in the yellow shirt in Figure 22 is approximately 6 ft tall. 

Figure 22 shows the complete assembly of the wind turbine 

in the laboratory setting.

Solar Panel 

Battery Pack—Because batteries for solar panels are 

12-volt and the power system is 24-volt, we were required 

to have four batteries in the configuration; two sets of batteries in a series and then the two pairs connected in parallel. 

Each individual battery had an estimated 225 amp hours 

and in the configuration of the battery bank was a total of 

450 amp hours. Using only 50% of the amp hours available 

and with a total load of roughly 7 amp hours, the battery 

bank could provide power to the security system for up to 

32 hours without charge from the wind and solar and with 

the security system running at 100% usage.

Controller—The controller used for this project was an 

off-grid controller designed specifically for the 600 vertical 

axis wind turbine (VAWT). The function of the controller is 

to take the variable 3-phase AC output from the permanent 
Covered Bridge Security Manual

27

magnet generator and convert it to a stable 24-volt DC output to charge a battery bank. The controller also manages 

the turbine so that it performs safely and optimally.

Diversion Load—The diversion load is designed specifically to work with the controller for this particular set up. 

If too much charge comes from the wind and solar units at 

any given time, the excess power goes to the diversion load, 

which dissipates power through the form of heat. This piece 

of equipment is essential so that the system is not overcharged, potentially destroying the controller or batteries.

Inverter—The inverter used with this renewable energy 

system was a 24-volt DC-AC pure sine wave. As mentioned 

earlier in this report, it is essential that a pure sine wave inverter is used when powering scientific equipment. The efficiency of the inverter was 89%; therefore, there was an 11% 

loss between DC to AC. This loss was accounted for in sizing stages so that the loss did not affect the security system.

Problems with Renewable Energy System

After installing the renewable energy, multiple problems 

arose with the power output of the system. The system could 

Figure 19. Original Hogback pole.

Figure 20. Wiring diagram for an off-grid system with solar and wind power.
General Technical Report FPL–GTR–223

28

shows the modified renewable energy system with the added 

solar panels. It can be seen from this photo that the extra 

solar panels are relatively large when compared with the 

original solar panel.

Holliwell

Located between Winterset and St. Charles, the Holliwell 

Bridge was the first bridge instrumented. An instrumentation pole was placed on top of a significant hill with heavy 

weeds between the bridge and the pole. An above-head power line was the power source for the surveillance system. A 

pole that was roughly 100 yards away had power already 

established and we decided that using overhead power lines 

would be easier and more efficient than trenching between 

the two poles.

As mentioned earlier, the heights of the NEMA enclosures 

vary between the different bridges and our initial thinking 

was to put the boxes high enough that they would be difficult for any vandals to tamper with but still be accessible 

with a ladder. After installing the box at the Hogback Bridge 

approximately 20 ft above ground, it was clear that this was 

not a safe situation for anyone doing maintenance on the 

system, and it was mostly likely not necessary if the boxes 

were appropriately labeled and securely locked.

Figure 24 shows one of the optimum positions for the flame 

detectors to be placed within the bridge. By side mounting 

the detectors, there was minimum interference with structural members and the best line of site was obtained. Most 

of the mounting positions at other bridges were somewhere 

between the side of the bridge and the middle of the opening as with the Cutler–Donahoe and Imes Bridges. As mentioned in the Cutler–Donahoe section of this report earlier, 

it is essential that the aesthetics of the bridge site and the 

functionality of the equipment are balanced.

Imes

The Imes Bridge used an existing pole that was moved 

roughly 20 ft from its original position. The NEMA enclosure was placed at chest height, which proved to be the most 

efficient height for protection while still allowing easy access into the enclosure. The flame detector was placed much 

like the Cutler–Donahoe set up in the middle of the bridge 

opening. Existing power for street lamps was roughly 50 ft 

away and was hand-trenched to the pole.

Roseman

The Roseman Bridge was one of the easier bridge set-ups 

because an existing pole in an optimum position that already 

had power available. This allowed for minimum disturbance 

with the aesthetic value of the bridge site, as very little had 

to be changed to install the security system. The flame detector was positioned halfway between the middle of the 

opening and the side of the bridge. Because of the architecture of the bridge, this proved to be the optimum position 

Figure 21. Assembly of 600-watt vertical axis 

wind turbine (VAWT).

Figure 22. Full assembly of 600-watt vertical 

axis wind turbine (VAWT).

not support the monitoring system that had been installed 

for more than 4 to 5 days. We decided to slowly start expanding upon the renewable energy system while trying to 

decrease the power demand from the monitoring system 

by turning off certain pieces of equipment during different 

times of the day. The first change to the system was the addition of two 230-watt solar panels as well as a controller 

that was used solely for these two solar panels. Figure 23 
Covered Bridge Security Manual

29

authorities such as police and fire departments that open 

flame tests will be conducted to ensure any alarms or notifications from passersby can be ignored during a certain time 

frame.

The test started in the middle of the bridge span directly 

between the two flame detectors on either end. For some of 

the detectors to be set off, the fire had to be pushed roughly 

10 ft toward the end of the bridge because the center of the 

bridge had some limitations to direct line of site.

The flame detectors were able to visually show that an alarm 

had been set off through the use of LED lights that could be 

seen through the wire mesh in the wooden boxes. A flame 

detector that is not set off and in working order is monitoring the bridge by blinking the LED lights every 15 seconds. 

Figure 26 shows a flame detector that was triggered during 

the fire testing. The red LED lights are constantly on and 

stay on until the system is reset via either internet connection or by simply cycling the power off and on.

After the flame detectors were found to be in working order, 

the same fire was started at the opening of the bridge on the 

side facing the IR and optical camera. Only the IR camera 

has the capability of setting off an alarm if a fire is present and there is no visual display to show if it is working 

properly as with the flame detectors. Once the IR camera 

would capture a temperature that exceeded the threshold 

temperature preset through the software, an email would be 

sent and the optical camera would capture a certain length 

of recorded video.

Example Case Studies

The creators of this manual decided to create multiple, 

fictitious case studies to show examples of how to implement different monitoring and security systems. These case 

studies show just one possible solution for each bridge. 

Numerous types of systems could be installed on each 

Figure 23. Modified renewable energy system (Compared 

with original system in Fig. 20).

Figure 24. Holliwell flame detector.

for the flame detectors with direct line of site to the middle 

of the bridge.

Testing

All five bridge sites were field tested to ensure that all 

equipment was operating properly. A 1-ft diameter pan was 

placed on a cart so a fire could be easily moved along the 

length of the bridge to ensure adequate fire-detection coverage. It should be noted that safety is the most important part 

of any in field testing that includes an open flame. Buckets 

of water and fire extinguishers should be close at hand as 

seen in Figure 25. It is also essential to inform all local 

Figure 25. Required material for flame test.
General Technical Report FPL–GTR–223

30

bridge depending on the requirements and financial 

resources available.

Slaughter House Covered Bridges

Bridge Owner

Town of Northfield

Bridge Location

Northfield, Vermont

Bridge History

The Slaughter House Covered Bridge is a 55-ft long queenpost truss bridge that carries traffic over Dog River by 

Slaughter House Road. This bridge was built in approximately 1872. This bridge is directly next to a highway and 

the local community is 1.5 miles away from the nearest fire 

department that has adequate equipment to put out a 

moderately sized fire on the bridge.

Figure 27 shows that the mid-span of the bridge is high 

above the Dog River below and virtually unreachable by local fire departments. This makes it more difficult to protect 

since a weakened mid-span can lead to total collapse. The 

lack of easy access deserves special consideration.

Security Option 1

Price: Low

Maintenance Required: Low-Moderate

Protection: Moderate

Equipment: Intumescent Coating, Signage

Because the covered bridge is close to a medium-sized 

city that has a fire department, the decision can be made to 

simply protect the bridge and reduce damage. By adding 

intumescent coating to the smaller bridge elements, such as 

the siding and roof structure, the bridge owner is drastically 

reducing the consequences of a fire. For added security, the 

bridge owner can decide to coat the structural members as 

well but because these members are harder to initially set, 

this may not be required. Adding signage to the bridge stating that the trespassers will be prosecuted will further increase the effectiveness of the security with little added cost.

Security Option 2

Price: Moderate

Maintenance Required: Moderate

Protection: Moderate-High

Equipment: Lighting, Flame Detectors

Adding a simple deterrent such as lighting can drastically 

reduce the chances that a trespasser will try to harm the 

bridge. This is especially true given the proximity to a major 

highway and a residential area. Because this option does not 

provide any protection, it is important that detection capabilities are high. This can be accomplished with the addition of 

flame detectors at one, or both, ends of the bridge. This will 

require higher maintenance with the addition of electronic 

equipment but will increase the security of the bridge.

Security Option 3

Price: High

Maintenance Required: Moderate

Protection: High

Equipment: Lighting, Sprinkler System

The most effective piece of equipment that could be used to 

protect this covered bridge is a dry pipe sprinkler system. 

Given the difficult accessibility, a sprinkler system could 

ultimately help the covered bridge survive if an arsonist was 

able to start a substantial fire before the fire department is 

alerted. Because this bridge is close to a residential area, we 

Figure 27. Side view of Slaughter House Covered Bridge.

Figure 26. Flame detector after alarm activation. 
Covered Bridge Security Manual

31

assume that a local water supply is close. Therefore, a hook 

up would not be as expensive as a more remote covered 

bridge. Adding lighting simply increases the protection of 

the security system by reducing the chance that a fire could 

be started in the first place.

Zacke Cox Covered Bridge

Bridge Location

Mecca, Indiana

Bridge History

The Zacke Cox Covered Bridge is a 72-ft single-span burr 

truss bridge built in 1908. It is in an isolated area with scattered farm houses in the vicinity. The nearest volunteer fire 

department is 4.9 miles away that has the capability of putting out a moderately sized fire.

Figure 28 shows a side view of the Zacke Cox Covered 

Bridge when the stream underneath it is completely dry. The 

stream is rarely completely full and can be easily walked 

across, allowing firefighters to get below the river and fight 

the fire from underneath the bridge if necessary.

Security Option 1

Price: Low

Maintenance Required: Moderate

Protection: Low-Moderate

Equipment: Intumescent Coating, Lighting

The simple addition of intumescent coating will reduce the 

chance that a major fire can occur at this bridge. The addition of intumescent coating on covered bridges is an attractive option for a bridge owner that does not want an expensive system or multiple pieces of electronic equipment. 

Maintenance will be required with this system but it will not 

usually require a completely new coat of intumescent 

coating for several years.

Security Option 2

Price: Moderate

Maintenance Required: Moderate

Protection: Moderate-High

Equipment: Intumescent Coating, Flame Detector

The addition of a flame detector will alert the fire department if a fire has been started on the bridge. This is important, as the fire department will have a 5-mile journey to get 

to the fire. Maintenance will be increased with the addition 

of a flame detector. However, this equipment will help to ensure that the fire department has as much notice as possible.

Security Option 3

Price: High

Maintenance Required: High

Protection: High

Equipment: Intumescent Coating, Flame Detector, IR 

Camera

The addition of an IR camera increases the level of protection from a fire by adding a level of security on the outside 

of the bridge. It can also be used to monitor individuals approaching the bridge at certain periods of the day. Given the 

remote location of the bridge, it is essential that all fires are 

detected as soon as possible. With the increase of electronic 

equipment, this will obviously increase the amount of 

maintenance required at the bridge site.

Real Case Studies

A national search was conducted to find different projects 

throughout the United States that included adding monitoring devices and different security equipment on covered 

bridge sites. Very few covered bridge owners were installing any monitoring devices, and a couple were adding other 

security systems such as lighting or fences. The majority of 

security installations dealt with structural strengthening and 

renovations to the bridges such as applying fire resistant materials to various components. These types of projects were 

not included in to the case studies as they did not add any 

sort of monitoring system on to the bridges.

Union County Covered Bridges

Bridge Names

Bigelow Bridge 

Pottersburg Bridge

Culberson Bridge

Bridge Owner

Union County Commissioners

Figure 28. Side view of Zacke Cox Covered Bridge.
General Technical Report FPL–GTR–223

32

Bridge Location

Union County, Ohio

Initial Price of Security System

$215,619.00 (for all three bridges)

Bridge History

These bridges in Union County, Ohio, have had arson and 

vandalism problems but nothing major to this point. There 

have been fire problems from people starting camp fires on 

the river banks under the bridges but nothing that appeared 

to be intentionally set.

Security System Overview

The security systems on these bridges use a linear heat detection cable located along the edges of the truss space as 

well as one cable down the center of the ceiling space. A 

Fenwall system with a Honeywell remote dialer was used 

for the linear heat detection system. Two cables also run the 

width of the bridge above the abutment areas of each bridge 

(Cable placement shown in above image). Once the detection cable is set off by a certain temperature, an audible 

and visual alarm is set off and an alarm is sent to the fire 

department.

All four bridges were also equipped with Tokistar LED 

lights that were modified to withstand vibration from traffic 

on the bridges. The LED lights were located under the roof 

to aesthetically wash down the walls of each bridge. The 

LED lighting is used to make the structures more visible 

with the hope of reducing the chances of someone damaging 

the bridge during nighttime.

Knecht’s Covered Bridge

Bridge Name

Knecht’s Covered Bridge 

Bridge Owner

Bucks County, Pennsylvania

Bridge Location

Springtown, Pennsylvania

Initial Price of Security System

$35,000.00

Source of Funding

Privately funded

Year Installed

2011

Bridge History

Bucks County has lost three covered bridges from arson 

since 1985 and almost lost another one when Knecht’s 

Covered Bridge was set on fire twice over a 3-year period with the last attack in 2007. Hay bales were placed 

on the bridge with a trail of accelerant and lit by a match. 

Fortunately for Bucks County, the hay was damp, so it 

smoldered instead of becoming set ablaze.

Security System Overview

The security system for the Knecht’s Covered Bridge 

included an alarm system with strobes and horns. These 

alarms are connected to a linear heat detection system that is 

controlled by a control panel enclosed in a NEMA 4 enclosure. There is also a dry standpipe sprinkler system across 

the length of the bridge to protect in case of any fire reaching a certain temperature threshold.

Pomeroy–Academia Covered Bridge

Bridge Name

Pomeroy–Academia Covered Bridge 

Bridge Owner

Juanita County Historical Society

Bridge Location

Port Royal, Pennsylvania

Initial Price of Security System

$16,600.00

Bridge History

It is unknown exactly when the Academia Covered Bridge 

was originally built, but this bridge was destroyed by ice 

floating down the river in 1901 and was promptly replaced 

with a new bridge that still stands today. In 1962, the 

Pomeroy–Academia Covered Bridge was scheduled to be 

completely destroyed and replaced with a new concrete 

bridge to span the river. The Juanita County Historical 

Society took prompt action and acquired the bridge and allowed it to stand.

In June 2009, weeks after $1.4 million was allocated for restoration of the bridge, suspected locals attempted arson. The 

individuals lit articles of clothing on fire and damaged some 

of the bridge deck. A few days later, the same individuals, 

as thought by the local police, returned to extensively spray 

paint graffiti throughout the bridge.

Security System Overview

An eight-camera security system was placed throughout the 

bridge site as well as within the bridge itself for a total of 

$14,000 and all the graffiti was removed and a coating of 

fire retardant was applied to the burned area for a total of 

$2,600.

Cedar Covered Bridge

Bridge Name

Cedar Bridge
Covered Bridge Security Manual

33

Bridge Owner

Madison County, Iowa

Bridge Location

Madison County, Iowa

Source of Funding

Federal

Bridge History

The Cedar Bridge was a major bridge in the 1992 book The 

Bridges of Madison County. In 2002, the Cedar Bridge was 

completely destroyed by arson. The town decided to rebuild 

the bridge with the same construction methods and materials 

as the original bridge and it was completed in 2004.

Security System Overview

An extensive security system was designed and installed 

on the Cedar Bridge with a grant from the USDA Forest 

Products Laboratory. This integrated system included an 

infrared camera, fiber optic temperature sensors, and two 

flame detectors at either end of the bridge.

Security System Technical Data

Major Equipment

One thermal imaging camera. 

Two electro-optical digital fire detectors were used with the 

specification of the detection of a 1 ft2 fire at 15 ft within 

5 s. Twelve fiber optic sensors. 

One optical sensing interrogator.

Additional Information

A detailed report for this project can be found in Remote 

Monitoring of Historic Covered Bridges (Phares and others 

2010).

Illinois Covered Bridges

Bridge Name

Red Covered Bridge 

Thompson Mill Covered Bridge

Bridge Owner

Illinois Department of Transportation

Bridge Location

Bureau County (Red Covered Bridge) 

Shelby County (Thompson Mill Covered Bridge)

Initial Price of Security System

$74,450.00 (Red Covered Bridge)

$71,090.92 (Thompson Mill Covered Bridge)

Year Installed

2005 (Both bridges)

Bridge History

Before the improved security systems were installed on this 

bridge, some basic light fixtures were located in the interior 

and openings of the bridges. These basic fixtures included 

three wall-mounted luminaires located inside the bridges 

and one pole-mounted luminaire on the North approach.

Security System Overview

Two light fixtures were installed on the bridge during the 

security system improvement. These light fixtures will be 

controlled by photocells that turn the lights on when the 

ambient light levels fall below a certain threshold. A single 

architectural floodlight on the south ensures that both approaches are lit. A triple architectural floodlight is directed 

at the existing parking lot. After the renovation to the lighting system, the interior of the bridge, both approaches, and 

the parking lot are completely lit during all hours of the day.

Along with the increased lighting are five cameras placed 

throughout the bridge site. A camera in the entrance on both 

the north and south side of bridge faces toward the center so 

the entire interior of the bridge is under surveillance. A camera on the ends of both the north and south approaches faces 

toward the entrances of the bridge. A camera is also mounted with the triple architectural floodlight facing towards the 

mechanical building.

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