“Good Enough” Bridges Aren’t Good Enough

Bridges are built to specific standards of weight and length of use, but these specifics and the laws surrounding them need to be reconsidered as times change and traffic increases.


| October 2016



Bridge

Present-day bridge design rarely considers the increasing number of cars and heavy trucks on the road, causing bridges to deteriorate and be rebuilt more frequently, and throwing off budgeting and advanced planning both locally and nationally.

Photo by Fotolia/dpmartin123

In America, our economy relies on roads, highways, and bridges. Yet the costs of construction and maintenance for these avenues climb while resources and funding drop off. In Henry Petroski’s book The Road Taken (Bloomsbury USA, 2016), the complex history and growth of the transportation industry is examined, as well as its flaws, its failures, and its future. From soaring structural feats that will engage engineers and economists, to the upkeep of residential roads sure to interest any homeowner, Petroski has a call to action when it comes to rebuilding our national prosperity in a way too often overlooked: infrastructure.

To find more books that pique our interest, visit the Utne Reader Bookshelf.

Bridge failures follow a cyclic pattern, occurring as they do after a prolonged period of unremarkable service. As I have written elsewhere, this period of perceived quality known as success lulls engineers into thinking they have solved all the relevant problems with bridge design and construction, and so they relax their guard, their standards, and their vigilance, meaning that they design less conservatively, build with less attention to detail, inspect more casually, and generally lower the quality of bridges being built. In the meantime, they also tend to push the limits of their technology, making longer spans and more daring new structures. The duration of success is typically remarkably close to three decades — about the extent of a professional generation — and by then complacency has become so common that any warning signs of impending disaster there might be are neither noticed nor heeded. When a major bridge failure does occur — like the destruction of the Tacoma Narrows Bridge in the wind in 1940 or the spontaneous collapse of the Minneapolis Interstate 35W bridge in 2007 — it is a clear wakeup call that complacency had indeed set in. Subsequent to the failure, engineers —  with the public and politicians looking over their shoulders — gain a new sense of urgency to design and oversee construction and maintenance with less carelessness and bravado and more quality and care. And so the cycle repeats.

Even given such a cycle, it is a fact that bridge failures are simply not very common. One major failure every thirty years is certainly no indictment that engineers and builders are without some considerable understanding of the workings of the daring structures that carry automobile, truck, and rail traffic across wide rivers and valleys. But the accusation of survivor bias with regard to praising the quality of older homes might make us wonder if such a phenomenon is also at play with regard to bridges. Were older bridges made better than newer ones? Any suggestion that they were is certainly counterintuitive. Nevertheless, we do celebrate ancient Roman aqueducts still standing in France and Spain; the countless centuries-old stone bridges still in service throughout Italy and the rest of the world; the first iron bridge, which has been standing since 1779 at Coalbrookdale, England; and, of course, the Brooklyn Bridge, which since 1883 has been faithfully serving New York City commuters.

At the same time, we see highway bridges that have served our interstates for mere decades being torn down after being replaced with newer, wider models. The multi-span Tappan Zee Bridge, when barely a half century old, was being replaced with a grand new crossing because the old steel cantilever was not considered up to current structural or functional standards or worth maintaining. And as we have seen, the east span of the San Francisco–Oakland Bay Bridge, which early in its sixth decade was damaged by an earthquake, was entirely replaced at a cost in excess of $6 billion. Did they or did they not really build them better in the old days?

The Eads Bridge across the Mississippi River at St. Louis is an iconic structure that in 2014 reached its 140th anniversary. The bridge had not been without trouble: its construction claimed the lives of fifteen men who worked in the pneumatic caissons driving the river piers down to bedrock; the bridge’s daring arches made of the new material steel were extremely difficult to complete; the bridge company went bankrupt within a year of the span being opened to traffic; part of the bridge’s east approach masonry arcade was destroyed by a tornado in 1896; railroads stopped using the bridge in 1974; and in 1991 its upper roadway was closed to motor vehicle traffic for major rebuilding. The structure was reopened to automobiles in 2003, a decade after its lower deck began to be used by Metrolink, the light-rail system that serves the St. Louis metropolitan area. Yet in spite of its vicissitudes, the Eads Bridge is a symbol of American innovation and resolve, and a clear success in its innovative use of the steel arch. It holds its own, even if as a low-profile architectural and engineering landmark in the shadow of the boldly soaring Gateway Arch.