The main theme of this issue of Informed Infrastructure is “bridges,” which allow people to cross rivers that used to be barriers. They provide a way to span a gap or valley rather than travel long distances around them. Bridges allow different modes of transportation to operate in the same space; connect areas previously separated; and offer opportunities for innovation in design and construction. These structures—often taken for granted—also can be admired simply for their beautiful shape or function.

A Long History of Bridges

Most likely, the first bridge was a log that fell across a creek. Some enterprising being in prehistoric times walked across a fallen tree and decided that it could be reproduced in another location. The first bridge engineer! One can only conjecture on the improvements made to this “design” over the next few thousand years.

One of the oldest working bridges, the Arkadiko Bridge, was found in Mycenae, an archaeological site in Greece, dating back to between 1300-1200 B.C. There are remnants of bridges in the area that may have been in existence in 1600 B.C. Although it’s true that these bridges were not complex, there was some basic understanding of the need for crossing some barrier as well as the thought process for figuring out how to get there.

Just a couple weeks ago, my wife and I had the opportunity to travel through parts of Europe. We saw the Charles Bridge, which was built in the 15th century over the Vltava River in Prague, Czech Republic. That same day, while on the train from Prague to Dresden, Germany, we went over a cable-stayed bridge over the Elbe River that probably was built just a few years ago.

The Charles Bridge carries thousands of pedestrians traveling from the Prague Castle to the town square on the east side of the Vltava. The cable-stayed bridge is one of many bridges enabling vehicles to cross a river for commerce and pleasure. Both are providing a means to connect two sides of a river. (If I were to bet on which one will still be in use 200 years from now, I would bet on the Charles …)

Bridge as Concept

Although there are numerous examples of bridges throughout history, I won’t pretend to be a bridge historian. I simply admire the work that has been done before me with fewer tools than I had at my disposal. But let’s spend a few moments thinking about “bridge” as a concept rather than construction project: the concepts of crossing barriers, spanning gaps, bringing things closer together, and two modes in the same space at the same time.

When I was working for the Indiana Department of Highways (IDOH), the local district reported that the bridge over the Wabash River in Peru, Ind., needed significant rehabilitation. The existing bridge was a steel truss bridge (two spans at 150 feet, if I remember correctly). It carried State Road 19 over the river and was too narrow, according to the standards in place at the time. Our policy dictated that we investigate options, including minor repairs, a full rehabilitation and a replacement. A repair wasn’t feasible, because it would only “buy us a few years.” A major rehabilitation would cost a significant amount—not as much as a replacement structure—but it would still be too narrow.

During the public hearing presentation, a few folks from Peru stressed the importance of the interaction between the communities north and south of the river as well as the length of time that the bridge crossing would be closed. One person said something very close to the following: “The two sides of Peru are separated by that bridge, and the residents of South Peru can’t afford to lose the business and inconvenience of the bridge being closed.”

It wasn’t too difficult to explain that the repairs would be somewhat temporary, and, although traffic could still flow across the bridge during repairs, the deteriorated condition would require a closing in the not-too-distant future. The length of closure (one construction season) and cost for rehabilitation and replacement were comparable.

But it was more satisfying to me to help them understand that it was the river that separated the communities and the bridge that connected them. It was therefore extremely important to do this project properly, so Peru remained properly “connected.” When the new bridge was opened to traffic, IDOH received a kind letter from the mayor, and an article in the local newspaper headlined: “North and South Peru Connected Again.”

There are many barriers that need to be crossed and gaps that need to be spanned. There seem to be more people that need to be brought closer together. Surely there’s a way for two different entities to exist in the same space. The bridges we design and drive over every day provide passage over obstacles. How can we, as engineers, be advocates for bridging gaps?