Bridges

Solutions

• Set a national goal that less than 15% of the nation’s bridges be classified as structurally deficient or functionally obsolete by 2013;
• Increase transportation investment significantly at all levels of government to fund the needed repair, renovation, or reconstruction of the nation’s deficient bridges;
• Implement an asset-management approach to maintaining bridges to achieve an appropriate balance between correcting immediate problems, conducting preventive maintenance, rehabilitating deficient bridges, and periodically replacing older bridges;
• Update bridge-inspection standards and implement risk-based prioritization for the repair or reconstruction of the nation’s bridges;
• Increase funding for long-term transportation research at the national level to ensure better performing and more resilient bridges.

Conditions

Usually built to last 50 years, the average bridge in our country is now 43 years old.1 According to the U.S. Department of Transportation, of the 600,905 bridges across the country as of December 2008, 72,868 (12.1%) were categorized as structurally deficient and 89,024 (14.8%) were categorized as functionally obsolete. From 2005–2008, the number of deficient (structurally deficient plus functionally obsolete) bridges in rural areas declined by 8,596. However, in urban areas during the same time frame, there was an increase of 2,817 deficient bridges.2 Put another way, in 2008 approximately one in four rural bridges were deficient, while one in three urban bridges were deficient. The urban impact is quite significant given the higher level of passenger and freight traffic.

A structurally deficient bridge may be closed or restrict traffic in accordance with weight limits because of limited structural capacity. These bridges are not unsafe, but must post limits for speed and weight. A functionally obsolete bridge has older design features and geometrics, and though not unsafe, cannot accommodate current traffic volumes, vehicle sizes, and weights. These restrictions not only contribute to traffic congestion, they also cause such major inconveniences as forcing emergency vehicles to take lengthy detours and lengthening the routes of school buses.

With truck miles nearly doubling over the past 20 years and many trucks carrying heavier loads, the spike in traffic is a significant factor in the deterioration of America’s bridges. Of the more than 3 trillion vehicle miles of travel over bridges each year, 223 billion miles come from trucks.¹

To address bridge needs, states use federal as well as state and local funds. According to the American Association of State Highway and Transportation Officials (AASHTO), a total of $10.5 billion was spent on bridge improvements by all levels of government in 2004. Nearly half, or $5.1 billion, was funded by the Federal Highway Bridge Program—$3.9 billion from state and local budgets and an additional $1.5 billion in other federal highway aid.¹ AASHTO estimated in 2008 that it would cost roughly $140 billion to repair every deficient bridge in the country—about $48 billion to repair structurally deficient bridges and $91 billion to improve functionally obsolete bridges.¹

Simply maintaining the current overall level of bridge conditions—that is, not allowing the backlog of deficient bridges to grow—would require a combined investment from the public and private sectors of $650 billion over 50 years, according to AASHTO, for an average annual investment level of $13 billion. The cost of eliminating all existing bridge deficiencies as they arise over the next 50 years is estimated at $850 billion in 2006 dollars, equating to an average annual investment of $17 billion.³

Resilience

The reliable and efficient flow of people, commodities, and emergency services within our roadway system relies on the nation’s bridge system, which overall is highly resilient. The keys involve three components: system redundancy and workarounds; recovery measures, including rapid restoration ability, security, and robustness against hazards—both natural and man-made; and individual bridges’ structural redundancy. Interstate bridges are usually built in pairs so that if one is taken out of service, the companion bridge can carry traffic in both directions temporarily. Also, in most urban areas, there are a number of bridges that can provide suitable alternate routes for traffic. Those key bridges that lack redundancy make it extremely difficult to establish convenient workarounds should the bridge be closed. Increasing congestion means that any rerouting caused by a significant bridge closure could result in major traffic delays.

Bridges are designed to account for the likely loads and forces that the span could expect to encounter during its service life. Structurally, today’s bridges are highly redundant, and incorporate multiple girder systems that can compensate for the failure of a single member. There are exceptions for example, fracture-critical bridges, which require more frequent monitoring to ensure that they remain capable of handling their designed traffic loads. Resiliency should be part of the evaluation criteria in a risk-analysis to justify and prioritize bridge investment. That investment includes activities that range from nonstructural measures to the structural and from the design of new bridges to the rehabilitation and replacement of old bridges.
 

Conclusion

While some progress has been made recently in improving the condition of the nation’s rural bridges, there has been an increase in the number of deficient urban bridges. At the same time, truck traffic over the nation’s bridges is on the rise—a matter of great concern as trucks carry significantly heavier loads than automobiles and exact more wear and tear on bridges.

The investment gap is accelerating and the failure to invest adequately in the nation’s bridges will lead to increased congestion and delays for motorists, wasted fuel, the further deterioration of bridge conditions, and increased safety concerns. Once Congress works to address these problems in the 2009 authorization of the Surface Transportation Program, it should establish a goal that less than 15% of the nation’s bridges be classified as structurally deficient or functionally obsolete by 2013 and should provide the funding needed to accomplish that.

Sources

1. American Association of State Highway and Transportation Officials (AASHTO). Bridging the Gap. July 2008
2. Data provided by Federal Highway Administration, U.S. Department of Transportation
3. Report of the National Surface Transportation Policy and Revenue Study Commission, Transportation for Tomorrow, December 2007 final report. Volume II, Chapter 4, p. 6