Built to last?

The American Society of Civil Engineers gave US bridges a C+ grade. But what does that really mean? 

On average, bridges are designed to last for 50 years. But of the country’s 614,387 bridges, nearly 40% have already hit this mark and gone past it. That’s nearly 240,000 bridges that are 50 years old or more, many of which were built under now outdated standards. This is a serious safety hazard, and yet technologically, it’s not a difficult problem to fix. Engineers have already identified how to bring the majority of these bridges up to modern standards. So then the question becomes: why haven’t we done it yet?

In a paper forthcoming in the Journal of Infrastructure Systems, titled “What Cannot Be Cured Must Be Endured: Understanding Bridge Systems as Institutional Relics,” recent Ph.D. alumnus Jaison Desai, now at US Army Cyber Command, and Assistant Professor Daniel Armanios in the Department of Engineering and Public Policy (EPP) argue that the problem isn’t just technological or financial—it’s also institutional.

“We propose reconceptualizing outdated bridges in the United States as institutional relics,” Desai and Armanios say. “‘Institutional’ because they are designed according to the standards formulated from the authoritative bodies of their time, and ‘relics’ in that the standards are built right into the structural properties of the bridge. Because of this, the repercussions of these standards persist even after they’ve been changed.”

One of the major deficiencies in these out-of-date bridge designs is the vertical clearance height. From 1951 to 1988, 14% of bridge failures in the US were due to collisions with low-clearance bridges. But why haven’t these bridges been corrected to federal clearance standards? The average construction year of these bridges is 1933, so they were built to the standard and vehicles of that time. As of 2012, there were still more than 52 million trips a day either over or under a bridge with a clearance of less than 14 feet—high enough for a car, but not a truck.

We propose reconceptualizing outdated bridges in the United States as institutional relics.

Daniel Armanios, Assistant Professor, Engineering & Public Policy, Carnegie Mellon University

In many ways, the long life of our infrastructure systems is an asset. We want our bridges to last. Yet, as Desai and Armanios write, when a bridge becomes an institutional relic, this longevity can actually become a liability. Because bringing already built bridges up to new standards can be very costly, bridge engineers are more constrained in updating existing bridges than in building new bridges that reflect the new standards. Cost is just one of a number of prohibitive factors that keep bridge managers from ensuring their structures are safe and up to date. Between budgets, the constraints of an urban space, and conflicting governmental interests—at local, state, and federal levels—it’s difficult to find a solution that works for both bridge users, and the managers who care for them.

“Identifying outdated bridges and their associated user costs helps diagnose and treat the symptoms,” they write in the paper, “but understanding the institutional constraints that prevent mangers from systematically addressing these issues can help explain why we still cannot fully arrive at a cure.”

This study has important implications for local, state, and federal bridge owners. Large-scale infrastructure projects require management of not just their structural elements, but their social elements as well—especially when considering future remediation as standards evolve. Moreover, to better understand the costs of addressing bridge infrastructure, policymakers need to think about them in the context of the time period in which they were built. The study identifies measurable factors to help bridge managers understand the social costs of a bridge system. This understanding can help them further target limited funds toward certain bridges, while avoiding those more difficult to salvage. This study may also translate to understanding other infrastructure system challenges such as scour remediation and local differences in load postings where there have been similar issues. 

Bridges are large-scale marvels of human engineering, but that isn’t all they are. They’re conduits for the complex social system that is modern society, and as such are subject to not just engineering but also institutional problems as well. From an engineering perspective, the myriad issues facing our country’s bridges are an easy fix. We already have the answers. But from a sociological perspective, these issues are much more complex, and their answers much more difficult to find. And according to Desai and Armanios, the only way we will find those answers is if we stop looking at the issue as simply an engineering issue. By incorporating sociological perspectives into engineering research, researchers and bridge managers can work together to ensure that the bridges of America’s future are as safe and modern as possible—and have the institutional capacity to keep it that way.

Learn more about Daniel Armanios' other research: