Bridges

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EXECUTIVE SUMMARY
There are more than 617,000 bridges across the United States. Currently, 42%of all bridges are at least 50 years old, and 46,154, or 7.5% of the nation’s bridges,
are considered structurally deficient, meaning they are in “poor” condition.
Unfortunately, 178 million1 trips are taken across these structurally deficient
bridges every day. In recent years, though, as the average age of America’s
bridges increases to 44 years, the number of structurally deficient bridges has
continued to decline; however, the rate of improvements has slowed. A recent
estimate for the nation’s backlog of bridge repair needs is $125 billion. Estimatesshow that we need to increase spending on bridge rehabilitation from $14.4
billion annually to $22.7 billion annually, or by 58%, if we are to improve thecondition. At the current rate of investment, it will take until 2071 to make allof the repairs that are currently necessary, and the additional deterioration overthe next 50 years will become overwhelming. The nation needs a systematic
program for bridge preservation like that embraced by many states, whereby
existing deterioration is prioritized and the focus is on preventive maintenance.

CONDITIONS & CAPACITY
Over the past decade, a concerted effort has been madeinvolving all levels of government to reduce the numberof structurally deficient bridges across the nation. While
structurally deficient bridges are not inherently unsafe,
they require substantial investment in the form of
replacement or significant rehabilitation, and they present
higher risk for future closure or weight restrictions.

considerably to just 0.1% annually, while the number ofbridges that are slipping from good to fair condition isincreasing annually. Though higher traffic volume bridges
tend to receive more attention and are therefore lesslikely to be structurally deficient, on average 178 million
trips occur over structurally deficient bridges every day.
At the current rate of improvement, it is estimated to takemore than 50 years, stretching to the year 2071, to repair
all of these bridges. This is not a sustainable model. The rateof deterioration is exceeding the rate of repair, rehabilitation, and replacement, all while the number of bridges
sliding into the “fair” category is growing. However,

Encouragingly, as of 2019, just one in 13, or 7.5%2 of
highway bridges were designated structurally deficient,or poor, representing a significant improvement from
12.1% recorded a decade ago. Also encouraging is thatthe total percentage of bridge deck area that is classified
as structurally deficient, or poor, has decreased over the
past several years, totaling just 5.5% in 2019, compared
to 6.3% in 2016.
Even with this renewed focus, nearly 231,000 bridges,
in all 50 states, still need repair and preservation work.
Unfortunately, the annual rate of reduction of structurally
deficient bridges for the past two years has slowed
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bridges categorized as fair are aconcern and an opportunity, as
they are potentially one inspection
away from being downgradedin classification, but they canalso be preserved at a fractionof the cost required to addressa structurally deficient bridge.

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Bridge Condition
By Year
300K

Number of Bridges

282,343
283,486

278,480

276,107200K

280,817

277,552

213,191
219,023

225,640

231,225

237,394

245,150

288,126

286,163

257,000

267,316

285,613250,858Good

279,504

291,339

282,319 279,582

Fair

100K

0
2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

Source: U.S. Department of Transportation, Federal Highway Administration, InfoBridge:
Data: https://infobridge.fhwa.dot.gov/Data/Dashboard

While recent improvements show a positive trend
To protect the public’s safety, the federal government
in addressing our poorest bridges, progress is notmandates national bridge inspections for all bridges on auniversal because states face different challenges
periodic basis. The amount of time between inspections
when maintaining, repairing, and replacing bridges.
can range from 12 to 48 months and is based on the
For example, in 2019, thebridge condition, type ofpercentage of structurally
While recent improvements bridge, traffic, location, anddeficient bridges ranged
age of the structure. If theshowapositivetrend
infrom 1% in Nevada to 22% in
bridge inspector finds any
addressing our poorest
Rhode Island.3
deficiency in the structural
capacity or with an element
bridges, progress is not
Less encouraging is thatof the bridge, that bridge
42% of the nation’s 617,084 universal because states face
be posted for load,different challenges when could
highway bridges are overweight, or speed restrictions;
50 years old, an increase
maintaining, repairing,
temporarily repaired; and/from 39% in 2016. Notably,
and replacing bridges.
or closed to the traveling
12% of highway bridges are
public to ensure their safety.
For example, in 2019, theaged 80 years or older.
percentage of structurally In 2019, just over 10% of
Structurally deficient bridges
bridges had such restrictions,deficient bridges ranged
specifically are nearly 69
a number that has remained
years old on average. Mostfrom 1% in Nevada to 22% stagnant over the past severalof the country’s bridges werein Rhode Island3.
years. Outside of direct
designed for a service life ofsafety concerns, posted
approximately 50 years, so
bridges can dramaticallyas time passes, an ever-increasing number of bridges will
increase driving time for larger vehicles such as school
need major rehabilitation or replacement.
buses, ambulances, fire trucks, and delivery trucks, in20________
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addition to interstate trucking. In rural areas, posted
bridges can prohibit the passage of emergency service
vehicles, which can slow response time and impede
rescue efforts.

horizontal clearances or inadequate approach roadwaygeometry. Such bridges do not serve current traffic
demand or meet current standards, and many of thesebridges act as bottlenecks, increasing congestion andcrash vulnerability due to inadequate widths, lanes, orshoulders, substandard vertical clearance, or insufficientlanes for traffic demand.

Finally, while the National Bridge Inventory no longer
tracks functionally obsolete bridges, there are still over
94,0004 bridges nationwide with inadequate vertical or

Photo Courtesy of WSP USA

FUNDING & FUTURE NEEDIn recent years, all levels of government have prioritizedbridge repairs through investments. To make many of theseinvestments, 37 states have either increased or reformed
their gas tax since 2010. However, despite states’
increased investments, overall spending in the country’s
bridges remains insufficient. The most recent Conditions
and Performance Report from the Federal Highway
Administration estimates the bridge backlog for repairs
for existing bridges at $125 billion and also estimates that
we need to increase spending on bridge rehabilitation by
58 percent from $14.4 billion annually to $22.7 billion
annually if we are to improve the condition.5

While state and local governments have demonstrated
initiative, federal investment in bridges remains stagnant.
As a result, the Highway Trust Fund, which historicallyfunds many of the nation’s road and bridge projects,
has been teetering on the brink of insolvency for over a
decade. The trust fund’s primary funding source is thefederal motor fuels tax, which has remained at 18.3 cents
per gallon since 1993. (See the Roads chapter for more
information regarding public spending.)

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INNOVATIONAs the nation’s bridges continue to age, America’s emphasis
has slowly evolved from building new bridges to maintaining
existing ones. New technologies, materials, evaluation
techniques, and construction methods have advanced
in recent years to meet this challenge. Additionally, theindustry manual provided by the American Association ofState Highway and Transportation Officials now requires
new bridges to be designed with a 75-year service life,
compared to the customary 50 years, meaning bridges
are now being built to last longer.

being used more widely, while new technologies such as
infrared thermography, ground-penetrating radar, andremotely operated surveillance devices like flying andsubmersible drones are being deployed to assess bridge
conditions and to facilitate safer, more efficient engineering
decisions. Additionally, engineers are designing “living
bridges” where sensors are being embedded into newand existing structures to provide continuous feedback
on structural conditions. Finally, prefabricated bridge
elements and Accelerated Bridge Construction are being
used with more frequency to reduce the amount of timetraffic needs to be disrupted while a bridge is repairedor replaced. All of these innovations, technologies, andevaluation methods are effectively allowing engineers
to identify problems earlier, increase the lifespan of thenation’s bridges, stretch limited resources, and prioritize
public safety.

Bridge engineers are now using materials such as
ultra-high-performance concrete, corrosion-resistantreinforcement, high performance steel, composites, andimproved coatings to increase resilience and add durability,
higher strengths, and longer life to bridges. Additionally,
minimal-impact, non-destructive evaluation methods are

As the nation’s bridges continue to age, America’s
emphasis has slowly evolved from building new bridges tomaintaining existing ones. New technologies, materials,
evaluation techniques, and construction methods haveadvanced in recent years to meet this challenge.
Photo: rinyun

CONCRETE COLUMNS AND RUSTY METAL OF THE OLD BRIDGE.

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OPERATIONS & MAINTENANCE

NearlyOur nation’s bridges comprise a vast, complex systemof unique structures, each of which is deteriorating at its
own pace and in need of specific treatments at specifictimes. In order to manage this large array of assets, states
are now required to develop and use Transportation AssetManagement Plans (TAMPs). The federally required
TAMPs outline a systematic, data-based approach forstates to manage their inventories. Each TAMP is required
to predict and set targets for the bridges that will be ingood or poor condition over the next 10 years. Strategic
asset management is one of the most cost-effective waysthat the nation is addressing its aging and deteriorating
bridge inventory.

21,000BRIDGES

were found to besusceptible to overtoppingor having their foundations
undermined during
extreme storm events.

One critical component of asset management is lifecycle cost analysis (LCCA). When the cost of a bridge
replacement, rehabilitation, or repair project is estimatedfor budgeting purposes without considering the longterm costs of maintenance, operation, replacement,
and retirement, decision-makers end up with anunderestimated value for their planning purposes. Because
bridges are costly and complex assets that provide decadesof service, the use of life-cycle cost analysis can minimize
long-term costs with a broad, upfront picture of the costs
over the infrastructure’s lifetime.

Photo by Joe Brady

RESILIENCE & PUBLIC SAFETY
As investments are made in the nation’s bridges, asystematic approach should be taken to make themmore resilient. Many of the country’s older bridges are
susceptible to extreme weather events and more prevalent
flooding, which can result in overtopping, washout, andother storm-related damage. In fact, nearly 21,000
bridges were found to be susceptible to overtopping or
having their foundations undermined during extreme
storm events. In seismic regions, earthquakes are asignificant threat, and a bridge’s ability to withstand these
extreme events is a significant safety issue.6

metal fatigue and cracking, and decrease the service
lives of bridges. The U.S. Department of Transportation
found that the introduction of double 33-foot trailer
trucks results in a projected 2,478 bridges requiringstrengthening or replacement at an estimated onetime cost of $1.1 billion.7 As future opportunities toplatoon connected or autonomous trucks become
more commonplace, bridges could see further stress.
Engineers are using new design requirements, materials,
and technologies to enhance the security and resilienceof bridges as they are being built. The great challenge
moving forward is to address the hundreds of thousandsof existing bridges so they can provide decades ofcontinued, safe service despite a greater frequency inextreme weather events or an increase in design loads.

Additionally, bridges are being subjected to trucks thatare heavier than those they were originally designed tosustain. These heavier trucks, which can surpass 40 ton
loads, threaten to overstress bridge elements, cause23________
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RECOMMENDATIONSTO RAISE THE GRADE

Bridges·

Increase funding from all levels of government to continue significant bridge repair,rehabilitation, and replacement.

·

Prioritize rehabilitating and preserving bridges in fair condition, as these bridges canoften be preserved at a fraction of the cost of replacement if the work is performed
in a timely manner. This approach can reduce the number of structurally deficient
bridges to below 5%, decrease the maintenance backlog, and address the large numberof bridges that have passed or are approaching the end of their design life.

·

Develop a balanced approach for our current aging bridge inventory that emphasizes
preservation, rehabilitation, and replacement where necessary, while also setting
aside funding for critical operation and maintenance. Bridge owners should consider
the costs across a bridge’s entire lifecycle (LCCA) to make smart design decisions
and prioritize maintenance and rehabilitation.

·

Fix the Highway Trust Fund by raising the federal motor fuels tax by five cents a year
over five years. In addition, to ensure long-term sustainable funding for the federal
surface transportation program, the current user fee of 18.4 cents per gallon on
gasoline and 24.4 cents on diesel should be tied to inflation to restore its purchasing
power, fill the funding deficit, and ensure reliable funding for the future.

·

Urge states to prioritize investments on bridges that are most critical, for example
those that experience the highest daily traffic volume, are on critical freight
corridors, evacuation routes, and develop multi-variable prioritization formulas forthe bridges in their state.

·

Advise states and the federal government to consider long-term funding solutions
for transportation infrastructure and potential alternatives to motor fuels taxes,
including mileage-based user fees.

·

Continue to fund research into the use of innovative technologies, materials, andconstruction techniques to extend the life of bridges and ensure they are climate
resilient.

DEFINITIONSSTRUCTURALLY DEFICIENT — Effective January 1, 2018, the Federal Highway
Administration (FHWA) changed the definition of “structurally deficient” aspart of the final rule on highway and bridge performance measures publishedon May 20, 2017, pursuant to the 2021 federal aid highway bill Moving Ahead
for Progress in the 21st Century Act (MAP-21). Two measures that were previously used to classify bridges as structurally deficient are no longer used. This
includes bridges where the overall structural evaluation was rated poor or worse
condition, or with insufficient waterway openings. The new definition limits theclassification to bridges where one of the key structural elements — the deck,superstructure, substructure, or culverts — are rated in “poor” or worse condition. Based on the new definition of structurally deficient, there are 6,533
bridges that would have been classified as structurally deficient in 2017 but did
not meet the new criteria in 2018.
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SOURCES

Bridges1.

American Road and Transportation Builder’s Association, Bridge Report, 2020.

2.

U.S. Department of Transportation, Federal Highway Administration, National
Bridge Inventory, 2019.

3.

U.S. Department of Transportation, National Bridge Inventory, 2020.

4. U.S. Department of Transportation, Federal Highway Administration, InfoBridge:
Data.
5.

U.S. Department of Transportation, Federal Highway Administration, “Status of
the Nation’s Highways, Bridges, and Transit Conditions and Performance Report,”
Chapter 7 – Capital Investment Scenarios – Highways, 23rd Edition.

6.

U.S. Department of Transportation, Federal Highway Administration, InfoBridge:
Data.

7.

U.S. Department of Transportation, Federal Highway Administration, MAP-21
Comprehensive Truck Size and Weight Limits Study, April 2016.

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