Transportation Network Robustness in an Era of Climate Change

There has been a lot of press lately, and justifiably so, on the recent multiday closure of the San Francisco Bay Bridge and the Lake Champlain Bridge (it looks as though this one will be permanently closed). Closures of such critical transportation links have played havoc on commuting times as well as on the local economies that they connected and bridged.

There has been little attention, however, given to the impact of the deteriorating transportation infrastructure on the environment.

Our paper, Environmental Impact Assessment of Transportation Networks with Degradable Links in an Era of Climate Change, which is the lead article in a forthcoming issue of the International Journal of Sustainable Transportation, provides quantitative measures to assess the impact on the environment of transportation infrastructure deterioration. It provides environmental impact assessment indices under alternative travel behavior (either system-optimal or user-optimal) and quantifies the environmental robustness of a transportation network subject to the deterioration of the roads, including their outright removal (as in the case of bridge closures or collapses).

The paper also demonstrates that travel behavior must be included in environmental assessments of transportation network robustness and the environmental impacts. In addition, and this is quite interesting, we demonstrate that system-optimizing behavior does not necessarily lead to reduced environmental emissions! Indeed, in certain networks, letting travelers behave selfishly and letting them determine their optimal routes of travel individually with no concern for negative externalities results in lower emissions than when a central controller routes traffic so as to minimize the total travel time!

Transportation networks are simply fascinating and counterintuitive phenomena associated with them from the Braess paradox on continue to provide important subjects for research, education, and, of course, practice.

Stmulus Package, Infrastructure, Cost-Benefit Analysis, Research

I was very pleasantly surprised that in today's New York Times, David Leonhardt, in his article, "A Stimulus with Merit, and Misses," writes that "in the current system, the federal government sends money to states without any real effort to evaluate whether it will pay for worthy projects." In regards to the new stimulus project to restart the US economy, he states: "They don't consider whether those new roads will lead to faster traffic or simply more traffic." "In the world of infrastructure, cost-benefit analysis is still a science of the future."

Leonhardt gets how important it is to do system-wide analyses of transportation "improvements" and "investments" a priori in order to ascertain where the funds can be best spent. I would also add to the discussion how can we improve transportation infrastructure so that the environment is at the same time not negatively affected but rather, over time, improved.

We have the results of our major scientific studies, now available, which address the above two issues. Our paper, "A Relative Total Cost Index for the Evaluation of Transportation Network Robustness in the Presence of Degradable Links and Alternative Travel Behavior," published in the first issue of 2009 in the International Transactions in Operational Research, vol. 16, pp. 49-67, provides rigorous, computer-based tools to assess the impact of tranport link degradation on system performance. The paper, "Environmental Impact Assessment of Transportation Networks with Degradable Links in an Era of Climate Change," in press in the International Journal of Sustainable Transportation goes further and captures the impact on the environment of the degradation of roads.

Good to see that more and more journalists such as David Leonhardt of the New York Times and Linda Baker (February 2009 Scientific American) get that "building more" does not equate with "building better!"