A look at the state of America's unsung infrastructure heroes
By Esri's StoryMaps team
Investing in infrastructure has, generally speaking, been a popular and productive decision by the United States government. It creates well-paying jobs, makes the country safer, and boosts the economy in a number of direct and indirect ways. That explains how, even in today's contentious times, a bipartisan, one-trillion-dollar infrastructure bill was passed by the United States Senate on August 10, 2021.
When thinking of infrastructure spending, it’s the brand-new, grandiose, far-reaching projects that often come to mind first—the kinds of things that entail a ribbon-cutting ceremony. However, it’s the upgrades to existing infrastructure, while less buzz-worthy and photogenic, that can provide the biggest return on investment. One type of infrastructure in particular carries an outsized importance: Bridges.
There are more than 618,000 motor-vehicle-carrying bridges in the United States.
If you’ve ever traveled in the U.S., you’ve almost certainly been across one or two of them—if not several hundred. From the vermilion arches of the Golden Gate to myriad industrious, commerce-sustaining highway overpasses, the bridges of the United States are a beacon of mobility, a triumph of modern engineering, and a critical component of the nation's expansive ground transportation infrastructure.
Bridges are so ubiquitous that they're easy to take for granted. Think about the last time you crossed one. Do you remember what it was made of? Do you know when it was built? Or what kind of condition it was in? How about the last time it was repaired or refurbished?
It’s perfectly normal to be unable to answer these questions, but they do make you wonder.
Take a look at a map of all 618,000 active motor vehicle bridges. At this scale, each bridge appears no larger than a pixel on the screen, hardly visible to the naked eye. But viewed in aggregate, they reveal a tapestry of dense urban areas connected by a sinuous network of roads—the fingerprints of modern development.
A static image of a map of the United States, with a small blue dot representing each of the country's 600,000-plus bridges
Bridges understandably tend to be clustered in and around major urban areas. Interestingly, though, there are areas—such as the Great Basin Desert in central Nevada—that do have concentrations of bridges despite lacking significant local populations. If you look closely enough, some of these arrays of bridges form a discernible network of sorts connecting big cities.
It's also worth noting is where bridges aren’t located. While the most iconic bridges span waterways or valleys or other natural features, bridges are conspicuously sparse near major physical obstacles like the lower Mississippi River.
The same map as the previous slide, with the Great Basin Desert and the lower Mississippi River circled and labeled
As these patterns reveal, bridges play an enormous but largely unsung role in our economy, commerce, and everyday life. It’s good to know that someone is paying attention to their well-being.
But to really understand the story of bridges—and what it takes to maintain them—it helps to examine their evolution and historical spread across the country.
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Bridges through time
Built before 1850
Mapped here are all of the still-operational roadway bridges built in the U.S. through the end of the 1840s. That was the decade during which westward non-indigenous settlement accelerated, forever changing transportation patterns and bringing about manifold technological advancements. These antique bridges are almost exclusively limited to the northeastern quadrant of the country.
During this period, many bridges were constructed out of sturdy stonework or masonry, which helps to explain their longevity. Others, especially in the New England region, took the form of wooden covered bridges.
A horizontal bar graph depicting the primary material used to build each still-operational bridge prior to 1850: Wood, 26; Stone, 93; Metal, 35; Other, 26
A sturdy stone bridge with two arches through which a rocky creek passes, seen from the banks of the creek
The Frankford Avenue Bridge in Philadelphia is the country's oldest surviving roadway bridge, dating to 1697. Today it still carries traffic on U.S. Route 13.
A static image of a map of the United States with blue dots representing every still-operational bridge that was built prior to 1850
1850-1899
By 1900, improved engineering methods meant bridges could be built larger and in greater numbers. While railroads were the primary driver of transportation infrastructure, the nation also started to see a rise in paved roadways for carriages, stagecoaches, and other forms of transportation.
Hundreds of the bridges that were built to service those modes endure to this day, again mainly in the more densely populated northeast and agricultural landscape of the Midwest.
A horizontal bar graph depicting the primary material used to build each still-operational bridge between 1850 and 1899: Wood, 222; Stone, 346; Metal, 749; Concrete, 207; Other, 6
A view of the impressive stone stanchions of the Brooklyn Bridge as the span stretches across to Manhattan's skyscrapers on a beautiful blue-skied day
The Brooklyn Bridge was an engineering marvel in its day. Upon completion in 1883, it was the longest suspension bridge in the world. It was also, remarkably, the first fixed crossing between what were two of the nation's three largest cities at the time: New York and a then-independent Brooklyn.
A static image of a map of the United States with blue dots representing every still-operational bridge that was built between 1850 and 1899
1900-1949
The rise of the automobile in the first half of the 20th century radically altered everyday life in America. A robust paved road network was built to support car and truck traffic, necessitating a slew of new bridges. Advances in steel and concrete production as well as new building techniques enabled construction of bridges that were longer and higher than ever before.
A horizontal bar graph depicting the primary material used to build each still-operational bridge between 1900 and 1949: Wood, 3,645; Stone, 1,014; Metal, 31,836; Concrete, 55,938; Other, 51
Bridges also became far more geographically widespread, reflecting changing patterns of industry and food production that drove much of American society through World War II. The highlighted bridges in this map were all built between 1900 and 1950 and are still in use.
The densest concentrations of new bridges occurred around hotspots of economic activity, including shipping (example: the Mid-Atlantic region); manufacturing (the steelmaking region of southwestern Pennsylvania); and agriculture (the Great Plains).
A static image of a map of the United States with blue dots representing every still-operational bridge that was built between 1900 and 1949. The Pittsburgh area is circled and labeled
Another major factor in bridge construction during this era was the plethora of economic stimulus measures enacted by the federal government under President Franklin Roosevelt during the Great Depression. Programs like the Works Progress Administration and the Civilian Conservation Corps invested billions of dollars in the country’s infrastructure under FDR’s New Deal.
The effects of such efforts can be plainly seen on the map—for example, in the cluster of bridges in central Tennessee and northern Alabama, a result of the work of the Tennessee Valley Authority, another New Deal agency.
The lit-up red towers and span of the Golden Gate Bridge stand out against an inky blue sky just before dawn
When it opened in 1937, the Golden Gate Bridge inherited the mantle of both the longest and the highest suspension bridge in the world. Spanning the Golden Gate Strait at the mouth of San Francisco Bay, its Art Deco stanchions are emblematic of a high point in American architecture. It continues to earn plaudits as one of the most iconic and photographed bridges in the world.
1950-1999
Of the 618,000 extant motor vehicle bridges in the United States, almost 400,000 were built between 1950 and the turn of the 21st century. This construction boom is largely explained by the advent of the Interstate Highway System.
President Dwight Eisenhower was a longtime, staunch believer in the need for a nation-spanning network of expressways similar to Germany's system of autobahns. In 1956, he signed the Federal Aid Highway Act (FAHA) into law, committing $25 billion dollars for the construction of over 40,000 miles of controlled-access highways.
A horizontal bar graph depicting the primary material used to build each still-operational bridge between 1950 and 1999: Wood, 12,283; Stone, 49; Metal, 116,150; Concrete, 269,520; Other, 89
With an emphasis on speedy travel, these roads were engineered to eliminate standard stop-and-go intersections. Thus, a new bridge was required every time a highway crossed paths with an existing road. This ultimately gave rise to the network of bridges sprawling across the U.S. in a grid-like pattern. The cost efficiency of concrete made it the material of choice during this massive expansion of the country's roads and bridges.
A photo of a highway through a canyon with sheer imposing rocky walls, from the point of view of the driver of a car on the highway. To the left is another portion of the highway, elevated on concrete stalks, while on the right is a river
Interstate 70 through Glenwood Canyon in Colorado was one of the final segments of the original plan for the Interstate system to be completed, opening in the early 1990s. Considered a remarkable feat of traffic engineering, the highway maximizes the limited space in the canyon by elevating the westbound lanes to partially overhang the eastbound ones as they hug the Colorado River.
2000-2020
Fast forward to the present day, and it's apparent that bridge construction continues apace. Concentrations of new bridges are especially noticeable in some of the country's fastest-growing metro areas: central and south Florida, urban Texas, Phoenix, and Denver, to name a few.
A horizontal bar graph depicting the primary material used to build each still-operational bridge between 1950 and 1999: Wood, 1,398; Stone, 5; Metal, 28,118; Concrete, 96,461; Other, 145
A histogram depicting the number of still-operational bridges built by year, from 1800 to 2020
This graph represents the number of active road bridges that were built in a given year. (The outlier spikes at five-year intervals result from generalized date estimates in the data.) The accompanying animation depicts the cumulative growth of bridges throughout the U.S.
Among the key takeaways from this temporal- and material-based analysis is that the vast majority of bridges are not, in fact, grand icons spanning dramatic natural features. Rather, they service a much more mundane and less glamorous purpose: the efficiency and expediency of everyday transportation and commerce, in the form of multilane highways.
Another observation is the modern prevalence of concrete as the primary construction material for bridges. Concrete, while initially cheaper and more environmentally sensitive to build with than, say, steel, tends to require an ongoing, more proactive care regimen to maintain its strength.
When the rubber hits the road
Every day, motorists make some five billion trips across America’s bridges. This map depicts them all, with bigger points representing more daily trips. Many of these crossings are undertaken by truck traffic, conveying everything from manufactured goods, to agricultural and food products, to raw construction materials.
In other words, without these bridges the United States would instantly crash to a halt, both socially and economically.
A map of the United States with each bridge now represented by an increasingly sized point based on how many trips are made across it each day. The metropolitan areas with the most daily trips are outlined and labeled. In order, they are: Los Angeles, New York, Dallas, Houston, Chicago
Inevitably, wear and tear from these billions of crossings eventually takes its toll. Roughly 1 out of every 13 of the bridges in the United States—about 46,000 in total—are considered to be in poor condition. These bridges aren't immediately unsafe, but they do require significant and sometimes urgent repairs. This map highlights the volume of daily trips taken across bridges in poor condition.
A pie chart depicting the percentage of bridges in the United States that are considered to be in good (45.0%), fair (47.7%), and poor (7.3%) condition
Every four years, the American Society of Civil Engineers (ASCE) assigns a letter grade to the different categories of public infrastructure in the United States based on its current physical condition and the amount of investment that would be required to get it up to acceptable standards. In the 2021 report card, America's bridges scored a C overall, underscoring the need for prompt investment.
The map of all bridges by daily traffic, except now those that are considered to be in poor condition are highlighted in a reddish tint. The metropolitan areas with the highest proportion of bridges in poor condition are outlined and labeled. In order, they are: Des Moines, Pittsburgh, Philadelphia, Chicago, New York
Looking for a quick fix
The total estimated cost to bring all bridges up to good condition exceeds $125 billion. At our current rate of investment, it would take another half-century to make all of the necessary repairs and rehabilitations. The bridges in poor or even fair condition require more prompt attention, which raises the question of how to strategically prioritize bridge repairs and refurbishments.
Aggregating bridges at the county level reveals clear regional trends. This map compares the total number of bridges in each county (indicated by the size of the circles) to the percentage of those bridges in poor condition. The brighter the circle, the greater the proportion of poor-condition bridges; duller shades indicate a lower percentage of bridges in poor condition.
Visualizing the data this way makes it easier to pinpoint areas of priority for investment.
For instance, it's possible to pick out counties—or even entire states—whose bridges badly need upgrades or repairs despite having relatively few of them. These places may be worth prioritizing because fewer bridges results in fewer travel alternatives if one bridge becomes unfit for motor traffic.
A map of the United States where every county is represented by a yellow circle symbol. The size of the symbol is determined by the total number of bridges in that county, while its shade of yellow is determined by the percentage of those bridges that are considered to be in poor condition (lighter shades mean a higher proportion of poor-condition bridges)
Cross-referencing bridges in poor condition with those approaching a century or more in age can help pinpoint bridges may be structurally obsolete and are nearing (or have already passed) the end of their design life. Repairing old bridges is typically costlier than applying preventative care to newer bridges, especially for those that have not yet crossed the threshold into poor condition.
A key question is where the money to perform sufficient repairs will come from. A lack of reliable, dedicated funding for bridge repair is an issue for virtually every municipality, county, and state. This uncertainty can lead to inefficient stopgap measures to maintain safe roads and bridges.
An extreme example of one such measure can be found in Pittsburgh. In the late 1980s, a nearly 70-year-old bridge began to crumble onto the Interstate highway below it. City officials initially fastened nets below the bridge to catch falling debris. The nets were not completely successful, however, so in 2003 the city erected a second, makeshift bridge under the existing bridge to provide additional protection to motorists. This solution made do for over a decade, until, at last, the old bridge was taken down and a brand new one built to take its place.
A multilane highway passes beneath a concrete arch bridge whose undersides are draped in dark netting. A smaller, boxy bridge below also extends over the highway
A nearly-completed concrete and steel arch bridge passes over an Interstate highway
The old Greenfield Bridge in Pittsburgh with its attendant mini-bridge underneath (left) and its just-completed replacement pictured in 2017 (right).
The future holds some promise for our aging bridges: Should the trillion-dollar infrastructure bill that’s currently on the table ultimately become law, it will represent the nation’s largest financial commitment to infrastructure since the New Deal. Approximately $110 billion of that expenditure would be earmarked for roads and bridges, the largest such promise since FAHA spawned the Interstate Highway system.
Explore the map
If you're interested in sinking your teeth into the bridge data used for this story, take some time to play with the map below. At smaller scales, the map shows the proportion of bridges in each county that are in poor condition (lighter shades indicate a higher percentage of poor-condition bridges). Click on a county to see some basic facts about its bridges. Zoom in to discover and explore hundreds of thousands of individual bridges.
The Frankford Avenue Bridge in Philadelphia is the country's oldest surviving roadway bridge, dating to 1697. Today it still carries traffic on U.S. Route 13.
The Brooklyn Bridge was an engineering marvel in its day. Upon completion in 1883, it was the longest suspension bridge in the world. It was also, remarkably, the first fixed crossing between what were two of the nation's three largest cities at the time: New York and a then-independent Brooklyn.
When it opened in 1937, the Golden Gate Bridge inherited the mantle of both the longest and the highest suspension bridge in the world. Spanning the Golden Gate Strait at the mouth of San Francisco Bay, its Art Deco stanchions are emblematic of a high point in American architecture. It continues to earn plaudits as one of the most iconic and photographed bridges in the world.
Interstate 70 through Glenwood Canyon in Colorado was one of the final segments of the original plan for the Interstate system to be completed, opening in the early 1990s. Considered a remarkable feat of traffic engineering, the highway maximizes the limited space in the canyon by elevating the westbound lanes to partially overhang the eastbound ones as they hug the Colorado River.
