The measurement and evaluation of the impacts, or indirect consequences, of alternative transportation investments in the Northeast Corridor are a subsystem of a total study. This paper describes the role of the impact modelling effort within the context of the total study and explains the strategy of, first, estimating the demographic, economic and land use consequences, and then the process whereby these forecasts are evaluated. The role of the decision-makers in this system is viewed as that of choosing between feasible, preferred (in an economic sense) transportation systems, given the estimated costs and benefits in a total (or general equilibrium) framework. The criteria established for the various phases of the effort, together with the limitations of the approach used, are also discussed.