Abstract
Transportation planning models are used in most American cities for evaluating potential transportation investments. This article claims that transportation planning models, as currently implemented, can produce results that are very misleading. Three examples are given to help illustrate that the common practice of assuming that future land use patterns are fixed,regardless of transportation infrastructure decisions, leads to substantial overestimation of societal benefits such as travel time savings, enhanced safety, and noise and pollution reduction. Better modeling solutions are available that incorporate land use feedback, so the task is to increase awareness of the problem and its solution among transportation professionals.