Clemson University in South Carolina is almost finished building a new pedestrian bridge that runs parallel to a four-lane road between the campus, where I work, and downtown, where I live. With big piles of dirt, heavy equipment and lots of rebar and concrete, it's the kind of construction site that excites us.

The finished product is going to look great and be much safer than the narrow sidewalk that was there before. As if that weren't enough, the bridge connects into Clemson's soccer stadium, my main source of entertainment in the fall. Still, walking past the bridge every day, I can't shake the thought that the project is irresponsible when it comes to meeting the principles of sustainable development.

Some of our best students and faculty studied this roadway a few years ago and suggested options, such as narrowing the road to two lanes or rerouting pedestrians through the center of campus to better meet user needs for less cost and with fewer resources. Because the design of the bridge project had been approved, these options were not chosen.

The pedestrian bridge is funded by the state and Clemson's athletic department, and both entities have reasons to prefer a bridge to other options. Our soccer stadium is now among the best in the country, and the striking design will ensure a spectacular opening ceremony.

Still, the bridge is a constant reminder of a question I have been grappling with for some time. What is our responsibility as designers and builders when the entire conception of the project violates principles of sustainable development?

I looked to the American Society of Civil Engineer's code of ethics for guidance. I already knew that we engineers should act in the best interest of the public, not just the client. And I knew that we should do what's right, not just follow laws. But I had to look up our sustainability obligations. Turns out, the very first "canon" in ASCE's code of ethics requires that we "strive to comply with the principles of sustainable development."

Should the professionals asked to design our pedestrian bridge have pointed out more sustainable options? What if those options require different design expertise? What about professionals asked to design and build a coal-fired powerplant? A 14-bedroom mansion for a bachelor billionaire? A LEED Platinum building, when user needs could be met with a more thoughtful use of existing spaces? If these examples can't be justified as sustainable, then are those who build them complying with our code of ethics?

An Unrealizable Ideal

Certainly sustainable development is an ideal that can never be fully realized. No project is perfect, and we can't stop building altogether. But people are already paying the price for our failure to address sustainability challenges and, in particular, climate change.

So, I don't know where we should draw the line on what we will design and build, but we must have one. Have you ever heard of a firm refusing a project because it violated the sustainable-development canon? When I was working in the industry, if you were paying, we were designing and building, no questions asked.