Q&A: Henry Petroski on roads, bridges, and traffic lights

Henry Petroski, Vesic Professor of civil engineering and professor of history, is the author of nineteen books—most recently, The Road Taken: The History and Future of America’s Infrastructure.

What’s the biggest surprise from your research on this book?

The fact that politics, finance, engineering, and lots of other forces—activism, environmentalism—push and pull infrastructure decisions in so many different directions. We should all be in it together for the common good. Infrastructure is, after all, public works.

How does America’s infrastructure compare with the rest of the world?

The American Society of Civil Engineers issues an infrastructure report card every four years; we keep getting a mediocre grade at best. That refers not just to roads and bridges but also to water supply, sewage, and so forth. Congress finally passed an infrastructure bill in early December, but it didn’t solve the central problem, the insolvency of the Highway Trust Fund. That fund is supported by the gas tax, but the gas tax has not been raised since 1993—even now that gas prices are very, very low. You can’t have good infrastructure without paying for it. In the early days of this country, you could get tax relief by working on the roads, maybe right in your neighborhood. People had a direct connection to the roads, and they saw that it took effort to put them in order.

Is it curious that we still have Roman-built roads to travel on?

Of course, the loads that were put on Roman roads didn’t include big semi-tractor-trailers. But we don’t build our roads of stone, and stone lasts a lot longer than asphalt. When you put a road down in asphalt, you’re going to have to replace it in a couple of decades, at most. So we’re not building for centuries.

You write admiringly of the Brooklyn Bridge. How common is it to see that kind of convergence of functional and aesthetic values?

It was rare even when the Brooklyn Bridge was built. That bridge’s designer, John Roebling, was not just a topnotch engineer; he also studied philosophy. Exceptional engineers back in the late 1800s saw bridges as monumental entrances to cities; they weren’t just utilitarian structures. And so they designed them for the ages.

You seem to be fascinated not just by big things, like the Brooklyn Bridge, but also by modest aspects of infrastructure, like centerlines and traffic lights. There are always challenges getting agreement around standards. What color paint do you use on centerlines?

Oregon wants one color; New York State wants another color. There have been debates about traffic lights. Should it be red light on top, green light on the bottom, or vice versa? There is one city with a large Irish-American community that didn’t like the red light on top—they wanted green, for Ireland, uppermost. That may be fine from a cultural point of view. But about 10 percent of male drivers are colorblind. They can’t distinguish between red and green light, except by their standardized position.

Are we going to see a future with different demands on infrastructure?

The technology for self-driving and interconnected vehicles is ready to go. But the public policy isn’t in place. If there is an accident with a driverless car, who’s at fault?

What’s your sense of how attentive Duke is to its infrastructure needs?

It’s variable. At the end of Science Drive, there’s a circle where buses, trucks, everybody can turn around. The buses ride up on the concrete curb and over time break off chunks of it. If campus planners had thought long term about the issue in the first place, they might have used granite. Now after a few years, they’ll say, “Oh, well, we should redo the curb.” There will likely be a patchwork repair—an incremental response to crumbling concrete—and the concrete won’t match. It’s what we see with the potholes we drive over, and it’s a metaphor for what’s happening with our infrastructure nationally.

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