Keeping America's Bridges Safe and Sound
Every day Americans drive millions of miles across the country’s 590,000 bridges with little thought about the structures. Bridges are so common that they melt into the backdrop of everyday life.
Supporting each of those bridges are not just piers and beams, but an entire network of engineers, inspectors, management systems, diagnostic equipment and inspection protocols to ensure their safety.
With the anniversary of the Minnesota bridge disaster, Americans no doubt will be wondering about the safety of the nation’s bridges. State departments of transportation (DOTs) devote thousands of employees and billions of dollars annually to measure, assess, maintain and repair the nation’s bridges to keep them safe and sound.
As a result, bridge failures are extremely rare. Of the few bridge collapses in recent decades, the large majority are attributed to external events such as ship collisions or major fires, or natural disasters such as earthquakes or hurricanes. According to the National Transportation Safety Board, in the past 20 years approximately 47 deaths have been attributable to bridge failures.
To state DOTs, any fatality or any bridge failure is unacceptable. That is why they inspect their bridges, invest in new diagnostic equipment and constantly strive to advance bridge design and materials.
Wearing Down the Nation’s Bridges
Traffic and age are two primary factors wearing down America’s bridges.
On an annual basis, more than 3 trillion vehicle miles of travel occur over bridges, with 223 billion miles of that travel occurring in trucks. Truck miles have nearly doubled in the past 20 years and are projected to grow steadily, adding significantly more loads to the already heavily traveled bridge system. Overall, freight volumes will grow from 16 billion tons today to 31 billion by 2025, with trucks continuing to carry approximately 60 percent of that tonnage on the nation’s highways and bridges.
The states are responsible for about 48 percent of the nation’s 590,000 bridges, including nearly all of the large, complex structures. Because the states manage the Interstate Highway System and National Highway System, more than 73 percent of all traffic is on state-owned bridges, and an estimated 90 percent of all truck traffic.
Not only have traffic volumes increased dramatically, but the nation’s bridges also are aging. The Interstate Highway System building boom from the mid-1950s to the mid-1970s led to the greatest bridge-building period in history. Many of those structures are approaching 50 years old and represent a sizeable need for additional investment—no matter how diligently they have been maintained.
The number of structural repairs needed on bridges increases proportionally with their age. Data from the National Bridge Inventory demonstrate how structural repair needs increase as bridges approach their 40th year. Today, about 50 percent of all bridges, when measured in terms of area, are between 35 and 55 years of age. While 50 years ago the nation faced an historic period of bridge construction, today it faces an historic period of bridge repair and reconstruction.
The nation’s Baby Boomer bridges are showing their age. The state DOTs are keeping these bridges safe with diligent inspections, improved materials and ingenious repairs. However, maintenance alone cannot sustain these bridges. A significant new investment and national commitment is necessary to protect these invaluable assets.
A Record of Progress Is Jeopardized by Rising Costs
For more than a decade, the nation’s departments of transportation were making steady progress on the nation’s bridge inventory—at least when measured in terms of structural repairs. From 1994 to 2004, bridge conditions in both rural and urban areas steadily improved. The U.S. DOT reported that overall deficiencies, and structural deficiencies declined in every road category, although functional obsolescence has remained relatively static. In 2001, 10 percent of all the nation’s bridges needed some type of structural improvement, while by 2007 that had dropped to 8.4 percent.
But this progress in improving bridge conditions is now jeopardized by unprecedented inflation in construction costs. With oil nearly quadrupling in price in the past four years, construction costs have soared. Asphalt prices have increased by 70 percent in the past five years, and diesel fuel, used for the operation of heavy construction equipment, is up by 63 percent in only a year. Overall, the costs of steel, asphalt, concrete, and earthwork have risen by at least 50 percent. In some places, such as Hawaii, they have doubled. This has seriously eroded the states’ ability to undertake planned construction projects at a time when so many bridges are in need of rehabilitation.
Summary
The nation’s bridge builders have created the largest inventory of bridges in the history of the world and have done so with great reliability and safety. However, that inventory is aging at a significant rate during a time of unprecedented cost increases. How to sustain this bridge inventory at safe and satisfactory levels is a critical issue for the nation.
Bridges Move People
Mississippi: Bay St Louis and Biloxi Bay Bridges: A Symbol of Hope and Recovery
On August 29, 2005, Hurricane Katrina hit the Mississippi Gulf Coast leaving in its wake a level of destruction the likes of which had not been seen before. Katrina unleashed more than $1 billion in damages to Mississippi’s transportation infrastructure alone. Two main bridges, the Biloxi Bay and Bay St Louis, were lost, impacting the daily lives of thousands people in and around the communities they served.
Traffic congestion became a nightmare as vehicles were forced to detour around the destruction to reach jobs, schools, and grocery stores. People like Mayor Chipper McDermot of Pass Christian, Mississippi, had to drive 55 miles round trip to get his children to school and back.
Both bridges reopened last year and McDermot says “We’ve been reconnected to our past and our future. People are coming back to their homes now and those that stayed can get to places faster and safer than we did before. I’m very pleased,” Mayor McDermot said.
Bridge festivals were held to mark the opening of the bridges, and thousands of people from the newly re-linked communities came out to celebrate this milestone in the recovery of the Gulf Coast. “I never thought a chunk of concrete would look so good. It brings tears to my eyes.” Chuck Breath, a Bay St. Louis resident, said of the new bridge.
