Thursday, November 12, 2009

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.