Civil Engineering: Easiest to Understand, Hardest to Do Right

When I joke about why people should go into civil engineering, I usually say because it’s the easiest branch of engineering. And from a technical perspective, it’s true. You’ll never have to do a Laplace transform or find that equations with imaginary numbers are the easiest way to understand the system. Unless you’re deep into materials science, you won’t have to understand much at a molecular level. Unless you’re a structural engineer, you won’t have to do very much in the way of mechanics. You won’t have to worry about designing and building things with dimensions accurate to the thousandth of an inch. Civil engineering has pretty high tolerances. No one here ever got hosed by being off by 10 nanometers.

The math behind civil engineering is really not very hard. If you understand simple geometry and algebra, you already know most of what’s needed. Many things we do, such as drainage design, deal with chaotic systems like turbulent water flow, which are best explained by empirical relationships worked out long ago. Like anything, some people have a natural talent for seeing how a road, rail, drainage system, or other facility should be laid out. But once you’ve laid it out, the calculations to see if it works are much simpler, at least in my mind, than trying to analyze something like an integrated circuit or an eccentrically braced frame.

However, civil engineering is unique in that the public plays a huge role in the day to day operation of our systems. Consider, for example, the electrical system in your house or apartment: you are given one voltage, available at fixed locations, with the interface designed to make it almost impossible to do it wrong. Or take an airplane or a chemical plant: use of the thing is restricted to a small group of trained people. Or something like a computer or a television: an extremely limited set of functions is available to the typical user (someone who doesn’t take them apart).

On the other hand, consider a road: practically anyone can get a license, and when they get out on the road, can do damn well near anything they please; just about everyone, of any age, is potentially a pedestrian. Or take a sanitary sewer system: people can, and will, put all kinds of things into a sewer besides sewage. Or a grade crossing: it is almost impossible to physically keep people off a railroad crossing when a train is coming.

This means that a large part of civil engineering is trying to understand human behavior. A design might make perfect sense from a technical perspective, and no sense from a human perspective. There are many classic examples of designs that are nominally better in the technical sense but worse in practice. A case frequently found in the US is the missing crosswalk – an intersection where crosswalks are only provided on three of the four approaches. This design works technically in that it increases the auto capacity of the intersection by eliminating a conflicting or time-consuming pedestrian movement, but practically it puts a perilously large amount of faith in the pedestrian to execute their part of the system according to the plan.

Beg buttons, especially in high-volume pedestrian areas, are another design that, um, begs to be violated. No doubt you have jaywalked when encountering such intersections. Transit stations that only allow entry at one end of the platform when the other end would also serve desired pedestrian movements are another example. These are not good designs and the fact that the pedestrian movement is illegal doesn’t make the design any better. You wouldn’t design a kitchen stove that set the walls on fire if you turned it up too high and then depend on the user to not turn it up too high.

The extensive interface with the public is one of the most challenging aspects of civil engineering, and it can be tempting to try to ignore it. Ultimately, though, we need to do better at relating our designs to expected behavior, because that will truly determine the success of a project.

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